Add realmd to critical-path-server
    
    It's part of domain enrolment (both FreeIPA and AD), which are
    release-blocking features for Server. Today a realmd update
    broke FreeIPA enrolment, which is causing tests for all Rawhide
    critical path updates to fail; if realmd had been in critical
    path itself we would have caught this and gated the update.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>