[Feature] Add support for OpenAI compatible providers

The Goal / Use Case

I would like to have custom OpenAI compatible providers. This would allow to add self-hosted routers e.g. 9Router.

Proposed Solution

Add a custom provider, named "OpenAI Compatible".

Potential Implementation (Optional)

The provider can be a copy of OpenAI. I'm currently using OpenAI with my 9router endpoint and key and works fine.

Impact & Roadmap Alignment

• This is a Core Feature
• This is a Nice-to-Have / Enhancement
• This aligns with the current Roadmap

Alternatives Considered

For now, just the workaround mentioned in the implementation section.

Additional Context

Can provide if any!