man: move from xmltoman to rst2man

xmltoman looks dead and uses XML as well as pulls in a long list of
Perl dependencies. This replaces it with rst2man that has almost no
dependencies beyond Python, which is already required for the Meson
build system.

Naturally rst2man uses reStructuredText and the pages were rewritten
via regex and manual editing to be as close to original XML format
as possible. A few fixes and updates were done too. Most notably a
note was added to indicate that production deployments should not be
starting the session manager via pipewire.conf file.

There's three slight formatting issues/differences:
1. rst2man produces simpler footer.
2. "-f | --foo=value" confuses the parser and it fails to correctly
   add argument specific syntax highlighting to assignment value.
3. XML version had inconsistent use of <arg> and <opt> which has
   been partially addressed. But different manual pages still have
   their differences to what and how is highlighted.