Pass metadata param to OpenAI client

[hoangtran98]

Hi team,

As I am looking to set up a proxy between agent server and openai server, I am going to need to pass in some metadata. So I can do some pre-checks before the request hits openai server. As of now, the current LLM interface doesn't support that. I think it'd be small changes that are useful for anyone looking to make use of metadata param from openai client.