ANTIBODIES TO HUMAN PROGRAMMED DEATH RECEPTOR PD-1 FIELD OF THE INVENTION The present invention relates to an antibody or antigen-binding portion thereof that can bind to human programmed cell death protein 1 (PD-1). The antibody according to the present invention is further used in the preparation of a drug for treating diseases in which expression of PD-1 is detrimental. BACKGROUND OF THE INVENTION PD-1 (CD279) is a 288 amino acid protein inhibitory receptor expressed on activated T-cells and B-cells, natural killer cells and monocytes. PD-1 is a member of the CD28/CTLA-4 (cytotoxic T lymphocyte antigen)/ ICOS (inducible co-stimulator) family of T-cell co-inhibitory receptors. PD-1 receptor has two ligands namely, Protein Death-Ligand 1 (PD-L1) and Protein Death-Ligand 2 (PD-L2). PD-L1 (CD274, B7Ή 1) is expressed widely on both lymphoid and non-lymphoid tissues such as CD4 and CDS T-cells, macrophage lineage cells, peripheral tissues as well as on tumor cells, virally-infected cells and autoimmune tissue cells. PD-L2 (CD273, B7-DC) has a more restricted expression than PD-L1, being expressed on activated dendritic cells and macrophages (1). PD-L1 is expressed in most human cancers, including melanoma, glioma, non-small cell lung cancer, squamous cell carcinoma of head and neck, leukemia, pancreatic cancer, renal cell carcinoma, and hepatocellular carcinoma, and may be inducible in nearly all cancer types (2). PD-1 binding to its ligands results in decreased T-cell proliferation and cytokine secretion, suppressing humoral and cellular immune responses and worsening of diseases where an active immune response would have otherwise alleviated the disease state. This immune suppression can be reversed by inhibiting the local interaction of PD- 1 with PD-L1, and the effect is additive when the interaction of PD-1 with PD-L2 is blocked as well (3, 4). Blocking PD-1 with antagonists, including monoclonal antibodies, has been studied in treatments of cancer and chronic viral infections (5). Monoclonal antibodies to PD-1 are known in the art and have been described, for example, in patent documents W02006121168, W02009114335, WO2008156712, WO2012145493, WO2015036394, WO2015112800, WO2016015685 and WO2018128939. Three antibodies targeting human PD-1 for the treatment of various cancers in combination with conventional drugs are available commercially. These three antibodies are nivolumab, pembrolizumab and cemiplimab. Despite the clinical success of anti-PD-1 antibodies, these therapeutic antibodies have several shortcomings, including the high cost, limited half-life and immunogenicity. Accordingly, there is a continued need in the field of PD-1/PD-L1 pathway based disease treatment with antibodies that can effectively bind human PD-1 and block its binding with PD-L1 or PD-L2 and also improve upon some of the challenges of existing therapies. The present invention discloses such novel antibodies. SUMMARY OF THE INVENTION The present invention provides novel anti -PD-1 antibodies that have one or more improved characteristics, e.g., relative to known anti-PD-1 antibodies used for therapeutic purposes. The anti-PD-1 antibody or antigen binding portion thereof of the present invention binds with high affinity to human PD-1. The amino acid sequence of constant region of anti-PD-1 antibody comprises of the IgGl, IgG2, IgG3, IgG4, IgA, IgE, IgM or IgD constant region, preferably the IgGl or IgG4. Further, one or more anti-PD-1 antibodies of the present invention has modified or reduced or no ADCC and /or CDC activity. In some of the aspects, the present invention provides anti-PD-1 antibodies which has high ADCC and /or CDC activity which may lead to lysis of PD-1 expressing cells. The anti-PD-1 antibody or antigen binding portion thereof of the present invention has a KD of 10-10 M or less, more preferably 10-11 M or less and even more preferably 10-12 M or less for a PD-1 antigen. KD value is a measurement of the binding affinity of the antibody towards its target antigen. The anti-PD-1 antibody or antigen binding portion thereof of the present invention can be used for the treatment of diseases where interaction of PD-1 with PDL1 and / or PDL2 is involved in modifying the disease state such as in infections and various cancers. In one aspect, the anti-PD-1 antibody or antigen binding portion thereof according to the present invention blocks PD-1 receptor interaction with its natural ligand PD-L1 and/or PD-L2. In another aspect of the invention, the anti-PD-1 antibody or antigen binding portion thereof kills the T cells that are expressing PD-1. Present invention also provides processes for preparing the novel anti-PD-1 antibodies and pharmaceutical compositions containing the same. BRIEF DESCRIPTION OF FIGURES Figure 1 depicts a general vector map of pZRCIIhyg Anti-PD-1 LC- HC vector construct which is used to prepare full-length monoclonal anti-PD-1 antibody of the present invention. Figure 2 depicts a general vector map of pSEX83 used in library generation to make anti-PD-1 Fab of the present invention. Figure 3 depicts a general vector map of pZRCIIIhyg Anti-PD-1 LC- HC vector construct which is used to prepare full-length monoclonal anti -PD-1 antibody of the anti -PD-1 Fab of the present invention. Figure 4 depicts the results of flow cytometry experiment demonstrating that anti -PD- 1 antibodies IP-H4.2L1, IP-H4L1 (IgGl) and IP-H4L1 (IgG4) of the present invention, directed against human PD-1, bind to PD-1 on the cell surface of human PBMCs. Figure 5 depicts the results of flow cytometry experiment using HEK 293 T cell lines demonstrating that anti-PD-1 antibodies IP-H4.2L1, IP-H4.19L1, IP-H4.36L1 of the present invention, directed against human PD-1, bind to PD-1 on the cell surface. Figure 6 depicts the results of flow cytometry experiment using HEK 293 T cell lines demonstrating that anti -PD-1 antibodies N5NL, N6NL, N7NL, N9NL and NIONL of the present invention, directed against human PD-1, bind to PD-1 on the cell surface. Figure 7 depicts the results of experiment demonstrating that anti -PD-1 antibodies IP-H4.2L1, IP-H4.19L1, 1P-H4.36L1 of the present invention, directed against human PD-1, promote Interieukin-2 (IL-2) secretion in a mixed lymphocyte reaction assay. Figure 8 depicts the results of experiment demonstrating that anti -PD-1 antibodies IP-H4.2L1, IP-H4.19L1, IP-H4.36L1 of the present invention, directed against human PD-1, promote IFN-gamma (IFN-g) secretion in a mixed lymphocyte reaction assay. Figure 9 depicts the results of experiment demonstrating that anti-PD-1 antibodies N5NL, N6NL, N9NL and NIONL of the present invention, directed against human PD-1, promote IL-2 secretion in a mixed lymphocyte reaction assay. Figure 10 depicts the results of experiment demonstrating that anti -PD-1 antibodies N5NL, N6NL, N9NL and NIONL of the present invention, directed against human PD-1, promote lFN-g secretion in a mixed lymphocyte reaction assay. Definitions The term“antibody” as referred to herein includes whole antibodies and any antigen-binding fragment (i.e.,“antigen-binding portion”) or single chains thereof. An“antibody” refers to a glycoprotein comprising at least two heavy (H) chains and two light (L) chains inter-connected by disulfide bonds, or an antigen-binding portion thereof. Each heavy chain is comprised of a heavy chain variable region (abbreviated herein as VH) and a heavy chain constant region (abbreviated herein as CH). The heavy chain constant region is comprised of three domains, CHI, CH2 and CHS. Each light chain is comprised of a light chain variable region (abbreviated herein as VL) and a light chain constant region. The light chain constant region is comprised of one domain, CL. The VH and VL regions can be further subdivided into regions of hypervariability, termed complementarity determining regions (CDR), interspersed with regions that are more conserved, termed framework regions (FR). Each VH and VL is composed of three CDRs and four FRs, arranged from amino-terminus to carboxy-terminus in the following order: FR1, CDR1, FR2, CDR2, FRS, CDRS, FR4. The variable regions of the heavy and light chains contain a binding domain that interacts with an antigen. The constant regions of the antibodies may mediate the binding of the immunoglobulin to host tissues or factors, including various cells of the immune system (e.g., immune effector cells) and the first component (Clq) of the classical complement system. The term“operatively linked” is intended to mean that an antibody gene is ligated into a vector such that transcriptional and translational control sequences within the vector serve their intended function of regulating the transcription and translation of the antibody gene. The term“Ka” & Kd are well known to a skilled person, wherein“Ka” is the association rate of a particular antibody-antigen interaction, whereas the term“Kd” is the dissociation rate of a particular antibody-antigen interaction. The term“KD” is an affinity rate constant, which is obtained from the ratio of Kd to Ka. It can be measured by using surface plasmon resonance method which is well known in the art. KD value is a measurement of the binding affinity of the antibody towards its target antigen. The term“KD” is also defined in WO 2006121168. This patent document is incorporated herein by reference. The terms“monoclonal antibody” or“monoclonal antibody composition” as used herein refer to a preparation of antibody molecules of single molecular composition. A monoclonal antibody composition displays a single binding specificity and affinity for a particular epitope. The term“bispecific antibody” refers to a homogeneous antibody population involved in the highly specific recognition and binding of a two different antigenic determinants, or epitopes. The term “recombinant antibody” according to the present invention, includes monoclonal antibodies which are generated recombinantly using synthetic heavy and light chain genes. Recombinant antibodies of this invention are monoclonal antibodies (mAbs) which are not produced using traditional hybridoma-based technologies, and do not need hybridomas and animals in the production process. The term“immune effector function” as used herein is a biochemical event that results from the interaction of an antibody Fc region with an Fc receptor or ligand. Effector functions include but are not limited to ADCC, ADCP, and CDC. The term also represents a physiological event such as circulating half-life of a drug or targeting of a drug to a particular cell or tissue type. The term“ADCC” or“antibody dependent cell-mediated cytotoxicity” as used herein is the cell-mediated reaction wherein nonspecific cytotoxic cells that express FcyRs recognize bound antibody on a target cell and subsequently cause lysis of the target cell. The term“ADCP” or“antibody dependent cell-mediated phagocytosis” as used herein is the cell-mediated reaction wherein nonspecific cytotoxic cells that express FcyRs recognize bound antibody on a target cell and subsequently cause phagocytosis of the target cell. The term“immune effector cell” as used herein is a cell that expresses one or more Fc receptors and mediates one or more effector functions. Effector cells include but are not limited to monocytes, macrophages, neutrophils, dendritic cells, eosinophils, mast cells, platelets, B cells, large granular lymphocytes, Langerhans' cells, natural killer (NK) cells, and gdT cells, and may be from any organism including but not limited to humans, mice, rats, rabbits, and monkeys. The term“Fc” fragment, whose name reflects its ability to crystallize readily. In human IgG molecules, the Fc region is generated by papain cleavage N-terminal to Cys 226. The Fc region is central to the immune-effector functions of antibodies. The term“Fc protein” as used herein refers to the portion of a single immunoglobulin heavy chain beginning in the hinge region just upstream of the papain cleavage site and ending at the C-terminus of the antibody. Accordingly, a complete Fc domain comprises at least a portion of a hinge (e.g., upper, middle, and / or lower hinge region) domain, a CH2 domain, and a CH3 domain. The term“pharmaceutical formulation” refers to preparations, which are in such form as to permit the biological activity of the active ingredients to be unequivocally effective. The term “pharmaceutical formulation” or“pharmaceutical composition” or“composition” can be used here interchangeably. The term“excipient” refers to an agent that may be added to a formulation to stabilize the active drug substance in the formulated form to adjust and maintain osmolality and pH of the pharmaceutical preparations. Examples of commonly used excipients include, but are not limited to, sugars, polyols, amino acids, surfactants, and polymers. “Pharmaceutically acceptable” excipients are those which can reasonably be administered to a subject mammal to provide an effective dose of the active ingredient employed. The term“treatment” or“therapeutics” as used herein, refers to any treatment of a disease in a mammal, particularly in a human. It includes: (a) preventing the disease from occurring in a subject which may be predisposed to the disease or at risk of acquiring the disease but has not yet been diagnosed as having it; (b) inhibiting the disease, i.e., arresting its development; and (c) relieving the disease, i.e., causing regression of the disease. The terms“patient” and“subject” are used interchangeably and are used in their conventional sense to refer to a living organism suffering from or prone to a condition that can be prevented or treated by administration of a composition of the present invention, and includes both humans and non-human animals. Examples of subjects include, but are not limited to, humans, chimpanzees and other apes and monkey species; farm animals such as cattle, sheep, pigs, goats and horses; domestic mammals such as dogs and cats; laboratory animals including rodents such as mice, rats and guinea pigs; birds, including domestic, wild and game birds such as chickens, turkeys and other gallinaceous birds, ducks, geese, and the like. The term does not denote a particular age. Thus, adult, juvenile and new bom individuals are of interest. An“effective amount” of an antibody of the invention, or composition thereof, is an amount that is delivered to a mammalian subject, either in a single dose or as part of a series, which is effective for inducing an immune response against target antigen in said subject. This amount varies depending upon the health and physical condition of the individual to be treated, the taxonomic group of individual to be treated and other relevant factors. It is expected that the amount will fall in a relatively broad range that can be determined through routine trials. A“pharmaceutically effective dose” or“therapeutically effective dose” is that dose required to treat or prevent, or alleviate one or more PD-1 related disorder or symptom in a subject, preferably in the present invention, for cancer or infection or autoimmune disease. The pharmaceutically effective dose depends on inter alia the specific compound (herein it is anti- PD-1 antibody or its combination or conjugate or bispecific) to administer, the severity of the symptoms, the susceptibility of the subject to side effects, the type of disease, the composition used, the route of administration, the type of mammal being treated, the physical characteristics of the specific mammal under consideration such as health and physical condition, concurrent medication, the degree of protection desired, and other factors that those skilled in the medical arts will recognize. Abbreviations of amino acids as used in the current application are provided in below table. Other abbreviations used in the present application: ACT: Adoptive cell transfer ADCC: Antibody-dependent cellular cytotoxicity ADCP: Antibody-dependent cellular phagocytosis CDC: Complement-dependent cytotoxicity CDR: Complementary Determining Region CFU: Colony forming unit CH: Constant region of heavy chain cHL: Classical Hodgkin Lymphoma CL: Constant region of light chain dNTP: deoxyribo Nucleotide Tri Phosphate ESCC: Esophageal Squamous Cell Carcinoma FACS: Fluorescence-activated cell sorting HC: Heavy Chain HCC: Hepatocellular Carcinoma HCVR: Heavy Chain Variable Region HEK: Human Embryonic Kidney hyg: hygromycin IFN-g : IFN -gamma LC: Light Chain LCVR: Light Chain Variable Region mAb: monoclonal Antibody MCC: Merkel cell carcinoma MLR: Mixed Lymphocyte Raction MOI: Multiplicity of Infection NSCLC: Non-Small Cell Lung Cancer PBMC: Peripheral blood mononuclear cells PD-1 / PD 1: Programmed cell death receptor 1 PD-L1 /PD LI: Programmed death ligand 1 PD-L2 / PD L2: Programmed death ligand 2 Pfx: Proof reading DNA polymerase, Pfx™ from Invitrogen. PMBCL: Primary Mediastinal Large B-Cell Lymphoma sRCA: Selective rolling circle amplification RCC: Renal Cell Carcinoma rpm: Round per minute SCCHN: Squamous Cell Carcinoma of the Head and Neck SCLC: Small Cell Lung Cancer SEQ / seq: Sequence SPR: Surface Plasmon Resonance VH: Variable region of heavy chain VL: Variable region of light chain EMBODIMENTS OF THE INVENTION The disclosure of the present invention relates to novel anti-PD-1 antibodies that can be used for therapeutic purposes. In one embodiment, the anti -PD- 1 antibody or antigen binding portion thereof of the present invention binds with high affinity to human PD-1. In one embodiment, the amino acid sequence of constant region of anti-PD-1 antibody comprises of the IgGl, IgG2, IgG3, IgG4, IgG2/G4, IgA, IgE, IgM or IgD constant region, preferably the IgGl or IgG4. In another embodiment, one or more anti -PD-1 antibodies of the present invention has modified or reduced or no ADCC and / or CDC activity. In one of the embodiments, the anti-PD-1 antibody or antigen binding portion thereof has reduced potential to cause the safety issue of ADCC and CDC. In another embodiment, the anti-PD-1 antibody or antigen binding portion thereof has ADCC and / or CDC activity. In another embodiment, one or more anti-PD-1 antibodies of the present invention has ADCP activity. In one of the embodiments, the anti-PD-1 antibody or antigen binding portion thereof of the present invention has a KD of 10-8 M or less, more preferably 10-10 M or less and even more preferably 10'11 M or less even more preferably 10-12 M or less for PD-1 antigen. KD value is a measurement of the binding affinity of the antibody towards its target antigen. In one of the embodiments, the anti-PD-1 antibody or antigen binding portion thereof of the present invention cross-reacts with PD-1 from species other than human. In one of the embodiments, the anti-PD-1 antibody or antigen binding portion thereof of the present invention has higher binding specificity towards human PD-1. In one of the embodiments, an anti-PD-1 antibody or antigen binding portion thereof of the present invention has an increased half-life in subject. In one embodiment, the anti-PD-1 antibody or antigen binding portion thereof according to the present invention blocks the function of PD-1. In one embodiment, the anti -PD- 1 antibody or antigen binding portion thereof according to the present invention prevents the binding ofPD-1 to PD-L1 expressing target cells. In one of the embodiments, the anti-PD-1 antibody or antigen binding portion thereof according to the present invention prevents the binding of PD-1 to PD-L2 expressing target cells. In another embodiment, the anti-PD-1 antibody or antigen binding portion thereof of the present invention kills the T cells that are expressing PD-1. In one embodiment, the anti-PD-1 antibody or antigen binding portion thereof according to the present invention has improved circulating half-life. In another embodiment, the anti-PD-1 antibody or antigen binding portion of the present invention is able to bind to the monkey PD-1 enabling ease of drug development by providing a relevant animal pharmacology and toxicology model. We claim: 1. An anti-PD-1 antibody or antigen binding portion thereof comprising: (a) CDRH1 of the general formula (I): X1a-A1a-X2a-A2a; (b) CDRH2 of the general formula (P) : A1b-C1b-A2b-C2b-C3b-A3b-C ,-C5b-C6b-C7b- X8b-A4b; (c) CDRH3 of the general formula (III): A1c-X1c-A2c-X2c-A3c-X3c-A4C-X5C-X5c-A5c; (d) CDRL1 of the general formula (IV): A1d-X1d-A2d-X2d-X3d-A3d-X4d-A4d-X5d-A5d; (e) CDRL2 of the general formula (V): A1e-X1e-A2e-X2e-A3e and (f) CDRL3 of the general formula (VI): A1fX1fA2fX2f -X3f X4f -X5fX6f wherein, X1ais an amino acid selected from asparagine, glycine and threonine; A1a is a dipeptide selected from Tyr-Tyr and Ile-Thr, X2a is an amino acid selected from isoleucine, leucine, valine, phenylalanine, methionine and alanine; A2a is single amino acid or dipeptide or tripeptide or tetrapeptide selected from tyrosine, asparagine, serine, glycine, Asn-Ser, Asn-Ser-Gly and Ser-Asn-Ser-Gly; A1b is optionally present and when present represents glycine; X1b is an amino acid selected from methionine, isoleucine, leucine, glycine, valine and alanine; A2b is tripeptide or tetrapeptide selected from Asn-Pro-Ser-Asn or Trp-Tyr-Asp; Each of X2b and X3b independently represents an amino acid selected from glycine and senne; A3b is single amino acid or dipeptide selected from lysine or Thr-Asn; X1b is an amino acid selected from tyrosine, arginine and phenylalanine; X5bis an amino acid selected from serine, tyrosine and asparagine; X6b may be optionally present and when present represents an amino acid selected from glutamic acid and glutamine; X7b may be optionally present and when present represents an amino acid selected from asparagine and lysine; X8b may be optionally present and when present represents an amino acid selected from tyrosine and phenylalanine; A4b may be optionally present and when present represents lysine; A1c may be optionally present and when present represents arginine; Xicis an amino acid selected from aspartic acid, asparagine and glutamic acid; A2c is an amino acid or dipeptide selected from asparagine, serine and threonine or Tyr-Arg; X2c is an amino acid selected from tyrosine, histidine, aspartic acid, glutamic acid, glycine and phenylalanine; A3c is an amino acid selected from aspartic acid, tyrosine, isoleucine, phenylalanine, histidine and tryptophan; X3c may be optionally present and when present represents an amino acid selected from isoleucine, leucine, valine, alanine, glutamine and methionine; A4c may be optionally present and when present represents glycine; X4c may be optionally present and when present represents an amino acid selected from tyrosine, histidine and phenylalanine; X5c may be optionally present and when present represents an amino acid selected from aspartic acid and glutamic acid; A5c may be optionally present and when present represents tyrosine; A1d is dipeptide or tripeptide selected from Gln-Ser or Arg-Ala-Ser, X1dis an amino acid selected from valine, glutamic acid and lysine; A2dis an amino acid selected from glycine and serine; X2d is an amino acid selected from isoleucine, leucine, valine, alanine, serine and methionine; X3d is an amino acid selected from serine, tyrosine and glutamic acid; A3d may be optionally present and when present represents an amino acid selected from threonine; X4d may be optionally present and when present represents an amino acid selected from serine, aspartic acid and glutamic acid; A4d may be optionally present and when present represents tetrapeptide Gly-Tyr-Ser- Tyr; X5d may be optionally present and when present represents an amino acid selected from isoleucine, leucine, valine, alanine and methionine; A5d may be optionally present and when present represents histidine; A1e may be optionally present and when present represents dipeptide Leu- Ala; X1eis an amino acid selected from serine, aspartic acid and glutamic acid; A2e is an amino acid selected from tyrosine or alanine; X2e is an amino acid selected from isoleucine, leucine, valine, alanine, serine and methionine; A3emay be optionally present and when present represents dipeptide Glu-Ser, Aif is dipeptide selected from Gln-His and Gln-Gln; X1f is an amino acid sequence selected from serine, arginine, aspartic acid and glutamic acid; A2f is an amino acid selected from arginine and serine; X2f is an amino acid selected from aspartic acid, asparagine and glutamic acid; Each of X3f and X5f independently represents an amino acid sequence selected from isoleucine, leucine, valine, alanine, tryptophan, arginine and methionine; X4f is proline; X6f is threonine, with the proviso that asparagine as Xu and methionine as Xu are not present together. 2. The anti-PD-1 antibody or antigen binding portion thereof as claimed in claim 1 comprising : (a) CDRH1 comprising amino acid sequence of the formula (la) :Xu-Y-Y-Xu-Y; (b) CDRH2 comprising amino acid sequence of the formula (Ha) :G-Xib-N-P-S-N- X2b-X3b-T-N-X4b-X5b-X6b-X7b- Xsb -K; (c) CDRH3 comprising amino acid sequence of the formula (Ilia) :R-Xic-Y-R-Xu-D- X3C-G-X4C-X5C-Y; (d) CDRL1 comprising amino acid sequence of the formula (IVa) iR-A-S-Xu-G-Xu- Xsd-T-Xw-G-Y-S-Y-Xsd-H; (e) CDRL2 comprising amino acid sequence of the formula (Va) :L-A-Xie-Y-X2e-E-S and (f) CDRL3 comprising amino acid sequence of the formula (Via) :Q-H-XirR- Xu - X3rP-X4rT wherein Xiais an amino acid selected from asparagine and threonine; Xu is an amino acid selected from isoleucine, leucine, valine, methionine and alanine; Xib is an amino acid selected from methionine, isoleucine, leucine, glycine, valine and alanine; Each of X¾ and C¾ independently represents an amino acid selected from glycine and senne; Each of Xib and Xgb independently represents an amino acid selected from tyrosine and phenylalanine; Xsbis an amino acid selected from serine and asparagine; Xeb is an amino acid selected from glutamic acid and glutamine; X7b is an amino acid selected from asparagine and lysine; Each of Xic and Xsc independently represents an amino acid selected from aspartic acid and glutamic acid; Each of X½ and X^ independently represents an amino acid selected from tyrosine, histidine and phenylalanine; Xsc is an amino acid selected from isoleucine, leucine, valine, alanine, glutamine and methionine; Xidis an amino acid selected from glutamic acid and lysine; Each of X2d and Xsa independently represents an amino acid selected from isoleucine, leucine, valine, alanine and methionine; Xaa is an amino acid selected from serine and glutamic acid; X4dis an amino acid selected from serine, aspartic acid and glutamic acid; Xieis an amino acid selected from serine, aspartic acid and glutamic acid; Xfeis an amino acid selected from isoleucine, leucine, valine, alanine and methionine; Xif is an amino acid sequence selected from serine, arginine, aspartic acid and glutamic acid; X2f is an amino acid selected from aspartic acid and glutamic acid; Each of Xgf and X