fix(docs): Improve documentation: drop-down for each version of skore

[sylvaincom]

We should think about how to provide documentation for each version of skore (like the drop-down selection of python documentation) in a final iteration.

Originally posted by @thomass-dev in #553 (comment)

This can be done very easily in the conf.py using the PyData Sphinx theme, see https://pydata-sphinx-theme.readthedocs.io/en/v0.15.4/user_guide/version-dropdown.html