Add support for slideshows using sphinx-carousel

sphinx-carousel is a Sphinx extension for creating slideshows using
Bootstrap carousels. The extension supports the PyData Sphinx theme that
we are currently using.

This would be a nice addition to show the various steps of an algorithm
in swh-alter documentation.

See: https://sphinx-carousel.readthedocs.io/ and
https://getbootstrap.com/docs/5.1/components/carousel/