Add ability to use other LLM providers

[anchapin]

I tried updating .env file to edit the base url for openai api so that I could utilize Z.AI coding plan such as described at https://docs.z.ai/devpack/tool/others but I can't get it to work.

I'm seeing:

                                                                                                                       
   | HTTPStatusError: Client error '401 Unauthorized' for url 'https://api.z.ai/api/coding/paas/v4/chat/completions'   
   For more information check: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/401 ```