Feat/support logit bias

[nguyenhoangthuan99]

Fix #263

request example:

  curl http://localhost:3928/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{
    "engine":"cortex.llamacpp",
    "logit_bias":{"12345":1},
    "model": "meta-llama3.1-8b-instruct",
    "n_probs":1,
    "stream":false,
    "top_k":20,
    "messages": [
      {
        "role": "user",
        "content": "Who won the world series in 2020?"
      },
    ]
  }'

Accepts a JSON object that maps tokens (specified by their token ID in the tokenizer) to an associated bias value from -100 to 100 (source: https://platform.openai.com/docs/api-reference/chat/create#chat-create-logit_bias)