[Platform][Gemini] Introduces support for gemini-2.5-flash-image and gemini-3-pro-image-preview models

[NicolasGraph]

It seems gemini-2.5-flash-image and gemini-3-pro-image-preview models do not work as for now. I get a Symfony\AI\Platform\Exception\ModelNotFoundException. It would be nice to support these models.

May be related: https://discuss.google.dev/t/404-not-found-unable-to-access-vertex-ai-gemini-3-pro-preview-in-europe-west8/288743

[chr-hertel]

Now supported in a first, flaky way - see #1054 and especially #1053

Help on this is pretty much welcome - in case you have some time to spend on improving your own use case :)