feat: update chat completion to send full tool call messages following openai lib

[IntelCoder0103]

Our currnet messages:

{
    "role": "assistant",
    "content": "...."
}

Assistant message with tool calls

{
    "role": "assistant",
    "content": "",
    "tool_calls": [
         {
               "id": "call_xxxx",
               "type": "function",
               "function": {
                   "name": "some_function",
                   "arguments" : {"arg1": "value1", "arg2": "value2"}
               }
         }
    ]
}

Tool message

{
    "role": "tool",
    "content": "Tool results ....",
    "tool_call_id": "call_xxxx",
}