Add support for siglip models

[xenova]

What does this PR do?

This PR adds support for exporting SigLIP models to ONNX. WIP for this issue.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint.

[xenova]

Got it working 🥳 huggingface/transformers.js#473

[xenova]

huggingface/transformers#26522 Is now merged into transformers!

[fxmarty]

@xenova can you push to this branch so that the CI is rerun?

[xenova]

Done ✅ (merged main)

[fxmarty]

Thanks! Not sure why we have

=========================== short test summary info ============================
FAILED exporters/onnx/test_onnx_export.py::OnnxExportTestCase::test_all_models_tested - AssertionError: Not testing all models. Missing models: {'siglip-text-with-projection', 'siglip-text-model'}

[Benjoyo]

Hey @xenova, any status on this? Can we get it merged? :)

I feel that this model is highly relevant and needs optimized inference :)