Support *_BASE_URL Environment Variables for LLM Providers

[Lition13]

Currently, Zed supports configuring LLM providers via environment variables such as ANTHROPIC_API_KEY, which is very convenient for secure and centralized configuration.

However, many users run LLM services through self-hosted gateways, proxies, or compatible third-party endpoints, which require overriding the default API base URL (for example, when using OpenAI-compatible or Anthropic-compatible services).

It would be very helpful if Zed could also recognize optional *_BASE_URL environment variables, such as:

• ANTHROPIC_BASE_URL
• OPENAI_BASE_URL
• MISTRAL_BASE_URL, etc.
  When present, Zed could use these values instead of the built-in default endpoints, similar to how API keys are resolved today.

This would:

• Enable easy use of self-hosted or proxy-based LLM services
• Improve parity with other tools that already support custom base URLs
• Keep credentials and endpoints fully managed via environment variables
  I believe this would significantly improve flexibility for advanced and enterprise users.
  Thanks for the great work on Zed!

[AmirHmZz]

Any updates on this?