[TRTLLM Python backend]Fix the output format for client side batching in dynamic batch

[sindhuvahinis]

Description

If the user sends, client side batch then the result is json array. If the user sends single input, then we send back json object.

Examples:
Request : "inputs":["The new movie that got Oscar this year"]
Response :

[
  {
    "generated_text":"The new movie that got Oscar this year is The Shape of Water."
  }
]

Request: "inputs":"The new movie that got Oscar this year"
Response:

{
  "generated_text":"The new movie that got Oscar this year is The Shape of Water."
}

[lanking520]

do we want to support client side batching? Maybe just server side is good enough

[sindhuvahinis]

do we want to support client side batching? Maybe just server side is good enough

We already do support. This PR just addresses the output format. In our CI, we also test client side batching. Today's CI would fail because the format is wrong.