.Net: New Feature: Add missing optional parameter responseMimeType to GeminiPromptExecutionSettings to allow for valid JSON output

[Millmer]

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name: Add missing optional parameter responseMimeType to GeminiPromptExecutionSettings

about: The optional API parameter responseMimeType is missing from the GeminiPromptExecutionSettings which is preventing the ability to have valid JSON responses returned from requests to Gemini (similar to OpenAI's response_format: "json_object"). This allows you to set the appropriate response type to avoid unintended behaviours.

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Suggested Property:

[JsonPropertyName("responseMimeType")]
[JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
public string? ResponseMimeType { get; set; }

Available values are:

• application/json: JSON response in the candidates.
• text/plain (default): Plain text output.
• text/x.enum: For classification tasks, output an enum value as defined in the response schema.

Google documentation:
https://cloud.google.com/vertex-ai/generative-ai/docs/reference/rest/v1/GenerationConfig
https://cloud.google.com/vertex-ai/generative-ai/docs/model-reference/inference

Ideally the responseSchema property should also be incorporated to allow for "controlled generation", as Google call it (the same as Structured Output with OpenAI), but that's a much larger implementation. Adding responseMimeType would be a great start and seems like a low handing fruit, I may be wrong though... 🤔 It looks like this has been added on the Python version already.

[shethaadit]

Hi @markwallace-microsoft, @moonbox3, I will work on this and raise PR soon. :)

[Millmer]

Thank you 🙏 I noticed a similar PR referring to the missing responseSchema property I mentioned: #9501

I'm not sure how I missed that one before making this one 🤔 🙃