Added Cosmos model files

[Tanuj-rai]

What does this PR do?

This PR adds up Cosmos (Nvidia) model files to the transformers repository.

Fixes #35565

Before submitting

• 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 write any new necessary tests?

Who can review?

@ArthurZucker and anyone in the community is free to review the PR.