Allow specify expected response type as JSON and pass schema

[taurit]

Is your feature request related to a problem? Please describe.

The most recent Gemini 1.5 API allows us to specify the exact JSON schema we expect for the response.

The SDK's current version doesn't allow users to request a response in JSON or pass the schema to the API.

Describe the solution you'd like

As a developer using the SDK, I would like to be able to specify the response type as JSON and provide the JSON schema:

var response = await geminiClient.TextPrompt(prompt, new GenerationConfig()
{
    MaxOutputTokens = 300,

    // Feature suggestion: add such property and pass the value to API as `response_mime_type`
    ResponseMimeType = "application/json",

    // Feature suggestion: add such property and pass the value to API as `response_schema`
    ResponseSchema = { ... // SDK could accept `JObject` or a string containing JSON}
});

Describe alternatives you've considered

Currently, I think the only alternative for this use case is to:

• not use the SDK,
• prepare a plain HTTP request using HttpClient or something similar.

Additional context

Google's documentation for ResponseMimeType and ResponseSchema doesn't contain examples of HTTP requests (only for SDKs in Python, Node, etc.).

I have experimented and provided examples of working requests to enable Gemini's JSON Mode on my blog.