The Sphinx configuration already supports both RST and Markdown via
myst-parser. Converting these docs to Markdown for consistency with
the rest of the tree.
Done with rst-to-myst plus manual fixups: replace eval-rst tables that
relied on RST substitutions with Markdown tables using inline HTML for
strikethrough/line-break, fix :ref: cross-references to use explicit
slug labels, and update the cross-doc link in index.md to use {doc}.
docs/config.yml warning patterns updated from .rst to .md.
Differential Revision: https://phabricator.services.mozilla.com/D304196