The WIP groups support is not complete yet, and won't work without extra
modules (which are not yet a part of Prosody). For now we hide --group support
unless mod_invites_groups (community module) is specified in modules_enabled.
This allows Prosody to easily provide friendly invitation links, even without
setting up mod_invites_page (which is a community module). Admins can
configure it to use a third-party deployment such as https://xmpp.link or they
can deploy their own based on
https://github.com/modernxmpp/easy-xmpp-invitation
Alternatively they can just install mod_invites_page and this will all be
handled automatically by that.
This makes it so that --admin and --role are no longer mutually
exclusive, they the former is simply treated as another --role.
This was likely a leftover from when only a single role was possible.
It does however become unclear which should be the primary, since the
order is not preserved by argparse.
Bonus: Loading of modules is avoided with only the --help is shown.