Fixes #36559 - Provide a systemd sysusers.d file

[ekohl]

The sysusers.d format describes the user and group which should exist. This allows admins to introspect which users should exist. In the future it can also make packaging easier because both RPM and Debian packaging can (on sufficiently recent versions) utilize this.

This uses /usr/sbin/nologin which today we already use on Debian. For RPMs we use /sbin/nologin but on EL8 realpath /sbin/nologin returns /usr/sbin/nologin so by using this we avoid resolving a symlink.

Currently a draft since I still need to do the packaging side of it.

[theforeman-bot]

Issues: #36559