Support to MimeType on gemini calls

[rossanodr]

Checked

• I searched existing ideas and did not find a similar one
• I added a very descriptive title
• I've clearly described the feature request and motivation for it

Feature request

It's possible to set the responseMimeType with ChatVertexAI

return new ChatVertexAI({
        model: model,
        responseMimeType: "application/json" | "text/plain"
        })

but it's not on ChatGoogleGenerativeAI, 'Object literal may only specify known properties, and 'responseMimeType' does not exist in type 'GoogleGenerativeAIChatInput'.'

Motivation

Gemini has some features available that are not possible using Vertex (it's not possible to set threshold: "BLOCK_NONE" as HarmBlockThreshold on Vertex).

Proposal (If applicable)

No response