Install PAM modules and systemd units from /lib to /usr/lib

Since Fedora 17 and about 2012, the directory /lib has been a symlink to /usr/lib. Debian started a similar migration in 2019. Nowadays all major Linux distributions have a merged /usr, and the canonical location for files should be /usr/lib instead of just /lib.

The location of PAM modules and systemd files is the last remaining part in MariaDB to fully complete the usr merge migration. Stable releases should not move files around, so target MariaDB 11.8 as the first release to have the /usr merge fully completed.

This task is supposed for deb packages, rpm-s are to be handled separately.

Pull request: https://github.com/MariaDB/server/pull/4065