Support functions/tools in OpenAI API about llm-on-ray

[carsonwang]

We can use mistral 7b to test this. It will also be useful to add a Langchain example that leverage this API.

[carsonwang]

@xuechendi is working on it.

[xuechendi]

@carsonwang, I've been working on this issue but a little lost on How to enable.
Observations:

1. HuggingFace support for 'tools', 'tool_choice': no native parameter support in generate function for "tools", "tool_choice". Seems huggingface has their own way to support Tools: https://huggingface.co/docs/transformers/main/en/custom_tools

2. RayLLM tools/tool_choice support. RayLLM supports these two keywords in client API, but after digging into inference codes, can't find how these two keywords passing to model.inference function either vLLMEngine or TRTEngine.
   Even though AnyScale blog mentioned their fully support for function_calls, it is not come to RayLLM codes yet. Anyscale Endpoints: JSON Mode and Function calling Features

3. llama_cpp toos/tool_choice support. I find function_call implementation in llama_cpp_python for two models: functionary and chatML. But only functionary is accepting these two keywords natually, chatML is still convert it as plain text as Langchain.initialize_agent did. https://github.com/abetlen/llama-cpp-python/blob/main/llama_cpp/llama_chat_format.py#L2032

4. vLLM / triton tensor-RT / huggingface issues research on tools/tool_chain support. Not found aligned conclusion.

Below is my branch for duplicating RayLLM supports for tools/tool_choice:
xuechendi@42d9613

[xuechendi]

pr: #134