update remaining Pop2Piano checkpoints

[susnato]

What does this PR do?

The remaining files are transferred to the original Pop2Piano repository on HuggingFace Hub (PR link).
This PR updates all the remaining checkpoints.

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

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Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
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[amyeroberts]

Thanks for updating!

[HuggingFaceDocBuilderDev]

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

[amyeroberts]

@susnato Am I OK to merge this - or are there other changes you'd like to push beforehand?

[susnato]

We can merge this.

BTW later this week I will update the pop2piano demo to use the transformers and also add some features to the space, is it a good idea to also add that at the end of the pop2piano.md file once it is finished, so we can showcase this model in a easier and interactive way?

[amyeroberts]

@susnato Great - yes, it'd be great to add examples for the model! For a spaces demo, this is normally added as a badge on the page e.g. like this for XLNet, and corresponding doc page.