Please add support for setting base_url

[maxmai-proactiveailab]

Is your feature request related to a problem? Please describe.
No

Describe the solution you'd like
The official Node.js and Python version of the OpenAI API client supports setting "base_url" property. A lot of other model hosting confronts to the OpenAI API protocol and the clients can just swap the endpoint URL "base_url" and API key to use a different LLM. Can you please expose that property in your library too? Thank you!

[maxmai-proactiveailab]

Python library example: https://github.com/openai/openai-python/blob/11460b5ed97080ee8e7a4311c1e90e495c59d370/src/openai/_base_client.py#L327