Add support for function call (response back) (message.role=tool)

# Add support for function call (response back) 1. Currently there's no support for sending back the function call result to the model using the `role=tool` messages. 2. Using the native API (not openai), function tool calls don't have an identifier associated `tool_call_id`, this is present in the `openai` API, and is important to be available on both APIs. > [!IMPORTANT] > This ID is very when providing the result back to the model (in a chat history where the same function was invoked multiple times in a chat history with different results) for the model to reason about.