Make Gemini API version configurable

[sberyozkin]

This is a draft PR as v1 does not recognize systemInstruction, tools and responseMediaType JSON properties

[geoand]

👍🏽

[geoand]

@sberyozkin is there something more that needs to be done on this one?

[sberyozkin]

Hi @geoand, I thought it would be an easy update (as far as I recall, Gemini 2.5 was not available with v1beta), but after I did it, I noticed those tags like tools were not recognized with v1, and then I started actually looking for the docs, and found:
https://ai.google.dev/gemini-api/docs/api-versions

According to that v1 does not support function calls yet. I think I saw somewhere that tools were renamed but I can't find that information again anywhere.

So I'm not sure right now how to evolve this PR. I checked with Guillaume as well. I guess we need to wait until some docs about how exactly function calls will be represented in v1 and then we'd have version specific generate content request/response support.

[sberyozkin]

@lordofthejars Hi Alex, have you seen some v1 specific migration guide somewhere, how tools are going to be represented, etc ?

[lordofthejars]

@lordofthejars Hi Alex, have you seen some v1 specific migration guide somewhere, how tools are going to be represented, etc ?

I have not looked at it. I know that tools is not working nowadays, but I have not checked.