Blockers for systemd in v25.06

Due to things like phosh, flatpak breaking badly due to upstream changes not reflected in systemd-services (!6044 (closed) #3475 (closed)), we need a better way than this. Things that I feel need to happen before we can publish systemd with v25.06.

• abuild's systemd subpackage support (@craftyguy is working on it)
  • moving systemd-services as much as possible to aports
• monitoring for outdated packages (WIP patch by @jane400 here, still needs a solution for pinging people actually)
• marking system units which need reloading/restarting, then applying it after upgrading everything.
  • this is probably best supported by systemd (systemctl daemon-reexec), we shouldn't touch unsupported services
  • things like https://src.fedoraproject.org/rpms/systemd/blob/rawhide/f/systemd.spec#_1138
  • things systemd_*with{restart,reload} in fedora

Optional, but we should really have this:

• usr-merge in alpine