This mimics what we already have for cryptsetup services: the slice they
are placed in (they have their own slice since that's what we do by
default for instantiated services) shouldn't conflict with
shutdown.target, so that veritysetup services can stay around until the
very end (which is what we want for the root and usr verity volumes).
It's literally just a copy of the same unit we already have for
cryptsetup, just with an updated description string.
This option is an indication for PID1 that the entry in crypttab is handled by
initrd only and therefore it shouldn't interfer during the usual start-up and
shutdown process.
It should be primarily used with the encrypted device containing the root FS as
we want to keep it (and thus its encrypted device) until the very end of the
shutdown process, i.e. when initrd takes over.
This option is the counterpart of "x-initrd.mount" used in fstab.
Note that the slice containing the cryptsetup services also needs to drop the
usual shutdown dependencies as it's required by the cryptsetup services.
Fixes: #14224
