[LEGACY] Create completion

curl --request POST \
  --url https://api.anyapi.ai/v1/completions \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "model": "<string>",
  "prompt": "<unknown>"
}
'

{
  "id": "<string>",
  "object": "text_completion",
  "created": 123,
  "model": "<string>",
  "choices": [
    {
      "text": "<string>",
      "index": 123,
      "finish_reason": "stop",
      "logprobs": {
        "tokens": [
          "<string>"
        ],
        "token_logprobs": [
          123
        ],
        "top_logprobs": [
          {}
        ],
        "text_offset": [
          123
        ]
      }
    }
  ],
  "usage": {
    "completion_tokens": 123,
    "prompt_tokens": 123,
    "total_tokens": 123
  }
}