[Feature Request]: Add structured_output to Gemini

[kim-borgen]

Feature Description

Hi,

Would it be possible to add a structured_output function to the Gemeni class?
https://github.com/run-llama/llama_index/blob/main/llama-index-integrations/llms/llama-index-llms-gemini/llama_index/llms/gemini/base.py

This can maybe be done by adding a generation_config to the send_message function, something like:

response = chat.send_message(next_msg, generation_config: Optional["genai.types.GenerationConfigDict"] = GenerationConfig(response_mime_type="application/json")

And some magic to add the pydantic object to the message somehow and then parsing the json to the pydantic object after, but I don't know the best approach.

Reason

No response

Value of Feature

Simplifying interaction with gemeni models.