Copyright
# What does this PR do?

This PR adds a copyright in any file missing, or fixes the copyright in some of the files to include HuggingFace when missing. We should be vigilant when new files are added to make sure they get one @LysandreJik and @patrickvonplaten 

I've excluded the examples folder as I'll do the copyright addition along with the cleaning.
Merging to avoid merge conflicts. Can address comments in a follow-up PR.