Replace Python script with Sphinx extension

[rgaiacs]

This is related to #825.

It moves the docs/_data/contributors/gen_contributors.py into docs/_ext/contributors.py and adapts the code to Sphinx extension.

As a Sphinx extension, we can write our own HTML.

[minrk]

Nice!

[rgaiacs]

This pull request can be preview at https://jupyterhub-team-compass--826.org.readthedocs.build/team/.

Before	After

I did my best to keep all existing features. Instead of use a script to write a file with the list of cards, the list of cards is built in memory. This should have little difference in the render time as the creation of files were always triggered. This will solve the problem with sphinx-autobuild given that no file in the source will change when creating the list of cards.

There are a little bit of duplication in the HTML across the .py files. I don't think that extra code refactoring worth to avoid the HTML code duplication.

I didn't check but I think that we don't use sphinx-design any more.