Migrate mkosi files from systemd-releng
    
    This includes the mkosi definitions from systemd-releng that are used
    for testing various stuff that can't be easily tested upstream at the
    moment, such as dracut, selinux-policy and upgrades from regular centos
    => hyperscale or upgrades from hyperscale => hyperscale.
    
    Some changes were made to get rid of deprecated settings and get the
    images building again with the latest mkosi.