Add ONNX export support for Chinese CLIP

[xenova]

What does this PR do?

As title says. Should be good to go since it's just a clone of the CLIP exporter.

Fixes # (issue)

Before submitting

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

[HuggingFaceDocBuilderDev]

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[fxmarty]

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

[xenova]

@fxmarty done ✅ (I just merged main)