OpenAI chat completions endpoint compatibility

[mcharytoniuk]

With Paddler 2.1 we introduced a boilerplate/stub compatibility endpoint that behaves like this one:
https://platform.openai.com/docs/api-reference/chat/create

It doesn't support all the fields, and tools for the moment. It would be good to have 100% compatibility with their API.

Currently the supported parameters are:

• max_completion_tokens
• messages
• stream

Parameters we won't support:

• model (it doesn't switch the model)

The remaining ones we need to add to Paddler.

What is required is to create a mapper that internally maps request parameters into Paddler parameters, then maps our response back into OpenAI format, similarly to this one: https://github.com/intentee/paddler/blob/ade9d9ada349f424dbe8ec281870eafaabe0c588/src/balancer/compatibility/openai_service/http_route/post_chat_completions.rs

If you want to help, and contribute to Paddler, this is a good place to start.