Push_to_hub in a pull request

[lhoestq]

Right now ds.push_to_hub() can push a dataset on main or on a new branch with branch=, but there is no way to open a pull request. Even passing branch=refs/pr/x doesn't seem to work: it tries to create a branch with that name

cc @nateraw

It should be possible to tweak the use of huggingface_hub in push_to_hub to make it open a PR or push to an existing PR

[nateraw]

Assigned to myself and will get to it in the next week, but if someone finds this issue annoying and wants to submit a PR before I do, just ping me here and I'll reassign :).

[AJDERS]

I would like to be assigned to this issue, @nateraw . #self-assign