New method for notebooks and docs

[mdbenito]

We cannot keep pushing notebooks with outputs for documentation. The obvious solution is to use git LFS but then we need to clean up the history and force push.

• [ ] Test in pipelines whether LFS things were pushed to git

[mdbenito]

Tested in https://github.com/mdbenito/pyDVL. I'll wait until we've merged all PRs and discarded any stale branches

[mdbenito]

~For the record, checkout seems not to pull LFS files despite lfs: true. Explicitly calling git lfs pull solves it of course. 🤷🏽~

I take that back. It was bfg not creating the .gitattributes properly (it incorrectly (?) adds braces around the file extension)

Steps to take:

1. Follow the steps here
2. Fix the .gitattributes removing the braces
3. add lfs: true to the checkout options in all github workflows

[mdbenito]

We need to do this ASAP, even if we don't use bfgs. We can just track notebooks in lfs and git add --renormalize . in the root. The history will still contain the stupid blobs from the past, but this is unsustainable.