Request to Add API Base Configuration for Google Gemini Model Provider

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Provide a description of requested docs changes

Hello, I noticed that when setting up "Model Providers," OpenAI has an "API Base" configuration option, but when setting up Google Gemini, there is only an API key setting and no "API Base" configuration option.

1. Could you add an "API Base" configuration option for Google Gemini?
2. Alternatively, could you point me to which source code file I need to modify to implement a custom API Base?

Thank you!