This commit removes the `home-manager-render-docs` package in favor
of upstream `nixos-render-docs` where the manpage generator has been
updated to take a `--header` and a `--footer` flag specifying static
content around the content derived from the options.json file.
The `optionsDocBook` function is deprecated in nixpkgs since
nixos-23.11. This commit updates the manual and manpages to
use commonmark formatted documentation instead of the deprecated
docbook format.
