Test RHEL UBI10, which runs systemd, on gVisor

redhat/ubi10-init covers a second systemd lineage: RHEL 10, systemd
v257, which mandates cgroup v2. The test boots it and checks for failed
units and a working transient unit.

images/systemd/ built systemd from source for a past investigation and
is referenced by nothing.

PiperOrigin-RevId: 970125419