Changes to Create Custom LLM

deleted the header request parameter x-api-key

the endpoint scheme security ApiKeyAuth was added to the API

added the new gemini enum value to the custom_llm/config/provider response property for the response status 200

added the new optional request property config/extra_parameters

added the new gemini enum value to the request property config/provider

added the optional property custom_llm/config/extra_parameters to the response with the 200 status

endpoint added