Openrouter integration

[Alexxosipov]

Hey, dear creator of the project! It would be nice to add support for openrouter LLMs as it becomes really popular and powerful solution.
Also openrouter accepts payments in crypto which I'm using a lot, so it is kinda difficult for me to pay for OpenAI API

[mikekelly]

This should be fairly easy to achieve but I don't have openrouter setup locally at the moment. If you want to have a go at it, it will likely look similar to this PR someone wrote which added support for ollama #5

[bpawnzZ]

I'm in the same boat. Can we set OpenAI base URL?? OPENAI_API_BASE

if so its is no problem to get Openrouter and LiteLLM working.