systemd: add proper User/Group
The Group= settings was ommited and default group of User= was implicitly used. Now the group set at build time is respected. GC didn't respect the user/group set at build time at all.
The Group= settings was ommited and default group of User= was implicitly used. Now the group set at build time is respected. GC didn't respect the user/group set at build time at all.