[DO NOT MERGE YET] Ensuring that the API returns None as the first token score in echo mode

Created by: punitkoura

Patch Description This change ensures that our API returns None as the first token score in echo mode. This is in line with how OpenAI API operates.

Testing steps Before the change

curl -k http://$ADDRESS/completions -H "Authorization: Bearer Punit"   -H "Content-Type: application/json"   -d '{
  "prompt": [133, 313, 1224, 15, 5, 856, 17527, 594, 4],
  "temperature": 1.0,
  "max_tokens": 0, "min_tokens": 0,
  "top_p": 1.0, "n": 1, "best_of": 1,
  "echo": true, "logprobs": 0, "seed": 1
}'  | jq .
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   775  100   578  100   197   1191    406 --:--:-- --:--:-- --:--:--  1594
{
  "choices": [
    {
      "logprobs": {
        "finish_reason": "length",
        "text_offset": [
          0,
          3,
          7,
          14,
          17,
          21,
          23,
          26,
          28
        ],
        "token_logprobs": [
          null,
          -3.4349148273468018,
          -5.929329872131348,
          -7.783979892730713,
          -3.8459229469299316,
          -1.0909258127212524,
          -4.3222551345825195,
          -0.008717338554561138,
          -0.018318286165595055,
          -2.4386134147644043
        ],
        "tokens": [
          "</s>",
          "The",
          " man",
          " turned",
          " on",
          " the",
          " f",
          "auc",
          "et",
          "."
        ],
        "top_logprobs": null
      },
      "text": "The man turned on the faucet."
    }
  ],
  "created": 1660233923,
  "id": "1aa3c12f-a3d1-4f5b-8025-3eb22a7dd3d3",
  "model": "30B/reshard_no_os/",
  "object": "text_completion"
}

After the change

curl -k http://$ADDRESS/completions -H "Authorization: Bearer Punit"   -H "Content-Type: application/json"   -d '{
  "prompt": [133, 313, 1224, 15, 5, 856, 17527, 594, 4],
  "temperature": 1.0,
  "max_tokens": 0, "min_tokens": 0,
  "top_p": 1.0, "n": 1, "best_of": 1,
  "echo": true, "logprobs": 0, "seed": 1
}'  | jq .
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   748  100   551  100   197   1960    701 --:--:-- --:--:-- --:--:--  2652
{
  "choices": [
    {
      "logprobs": {
        "finish_reason": "length",
        "text_offset": [
          0,
          3,
          7,
          14,
          17,
          21,
          23,
          26,
          28
        ],
        "token_logprobs": [
          null,
          -5.929329872131348,
          -7.783979892730713,
          -3.8459229469299316,
          -1.0909258127212524,
          -4.3222551345825195,
          -0.008717338554561138,
          -0.018318286165595055,
          -2.4386134147644043
        ],
        "tokens": [
          "The",
          " man",
          " turned",
          " on",
          " the",
          " f",
          "auc",
          "et",
          "."
        ],
        "top_logprobs": null
      },
      "text": "The man turned on the faucet."
    }
  ],
  "created": 1660233768,
  "id": "01c269be-0096-4154-b132-51fd5419f95d",
  "model": "30B/reshard_no_os/",
  "object": "text_completion"
}

Note that after the change, we do not return a score for (and trim it from the returned tokens), and set the score for the first word "The" to None (instead of -3.4349148273468018)

A similar change is made for top_logprobs. After the change

curl -k http://$ADDRESS/completions -H "Authorization: Bearer Punit"   -H "Content-Type: application/json"   -d '{
  "prompt": [133, 313, 1224, 15, 5, 856, 17527, 594, 4],
  "temperature": 1.0,
  "max_tokens": 0, "min_tokens": 0,
  "top_p": 1.0, "n": 1, "best_of": 1,
  "echo": true, "logprobs": 2, "seed": 1
}'  | jq .
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  1196  100   999  100   197   3517    693 --:--:-- --:--:-- --:--:--  4211
{
  "choices": [
    {
      "logprobs": {
        "finish_reason": "length",
        "text_offset": [
          0,
          3,
          7,
          14,
          17,
          21,
          23,
          26,
          28
        ],
        "token_logprobs": [
          null,
          -5.929329872131348,
          -7.783979892730713,
          -3.8459229469299316,
          -1.0909258127212524,
          -4.3222551345825195,
          -0.008717338554561138,
          -0.018318286165595055,
          -2.4386134147644043
        ],
        "tokens": [
          "The",
          " man",
          " turned",
          " on",
          " the",
          " f",
          "auc",
          "et",
          "."
        ],
        "top_logprobs": [
          null,
          {
            " first": -4.359017372131348,
            " only": -3.9527673721313477
          },
          {
            " is": -2.362104892730713,
            " who": -1.5808547735214233
          },
          {
            " his": -2.4084229469299316,
            " into": -2.2209229469299316
          },
          {
            " his": -1.4503008127212524,
            " the": -1.0909258127212524
          },
          {
            " TV": -2.9472548961639404,
            " water": -2.5878798961639404
          },
          {
            "auc": -0.008717338554561138,
            "ount": -6.1024675369262695
          },
          {
            "et": -0.018318286165595055,
            "ets": -4.033943176269531
          },
          {
            " and": -1.1573634147644043,
            ",": -1.7042384147644043
          }
        ]
      },
      "text": "The man turned on the faucet."
    }
  ],
  "created": 1660235018,
  "id": "0144410a-a8f5-48ea-8955-df9ad1da7b7e",
  "model": "30B/reshard_no_os/",
  "object": "text_completion"
}