Refactor all metadata into pyproject.toml

This PR refactors all project metadata into the singular pyproject.toml file and removes the setup.cfg and setup.py files.

This requires a number of updates to the packaging for Red Hat and Debian, including hacks to reinstate the setup.* files to accommodate old versions of setuptools, argparse-manpage, etc. Hopefully these are written and labelled in such a way as to make removing them easy enough when updated versions are available.