Split systemd-container, reconsider inclusion or exclude qemu (recommends)

Since recent systemd commits (rawhide, f41), systemd-container now recommends qemu (qemu-kvm right now, qemu-kvm-core soon) for systemd-vmspawn.

We included systemd-container in https://github.com/fedora-silverblue/issue-tracker/issues/503 to bring the machinectl command line tool which is useful to run command as other users in a safe fashion.

We don't expect Atomic Desktops users to run systemd-vmspawn so we could:

• exclude systemd-container entirely
• ask for machinectl to be split from it
• exclude the qemu and related packages as they are only recommended

See also https://github.com/fedora-silverblue/issue-tracker/issues/522.