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/