T5gemma2

[bzhangGo]

What does this PR do?

Add support for T5Gemma2 with multi-modal and long-context capability.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

[github-actions]

[For maintainers] Suggested jobs to run (before merge)

run-slow: auto, t5gemma, t5gemma2

[Rocketknight1]

Hey! Is this a pre-release model? I don't see the checkpoints like google/t5gemma-2-270m anywhere

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[bzhangGo]

Hey! Is this a pre-release model? I don't see the checkpoints like google/t5gemma-2-270m anywhere
yeah, coming soon