Add Collection API (create, list, add to collection, delete?)

[Wauplin]

Collections are a new way to aggregate models, datasets, spaces and papers in a single "collection" page. For example: https://huggingface.co/collections/TheBloke/recent-models-64f9a55bb3115b4f513ec026

Would be great to add support for it in huggingface_hub. It still requires some work on the backend to make the API accessible via a user access token.

Mostly a utils to add for power users but still great as it helps discoverability on the Hub. No need to implement everything at once. Creating and updating a collection (add/remove item) should be the priority.

[julien-c]

also in the same issue (i guess) to document the endpoints in hub-docs/api.md =)

bonus: revamp the ugly table in that document:)

[Wauplin]

Re: revamp the ugly table in that document:) Let's start with that and iterate once we agree on the layout. Opened a PR there: huggingface/hub-docs#962.

[Wauplin]

I opened a separate issue for the hub-docs part: huggingface/hub-docs#967. Will close this issue now as the huggingface_hub is now complete.