Backup ipa-specific httpd unit-file
    
    On backup-restore, the ipa unit file for httpd was not backed up.
    This file however contains setting for httpd to communicate with
    gssproxy so not backing it up will result in httpd not knowing
    how to get credentials.
    
    https://pagure.io/freeipa/issue/6748
    
    Reviewed-By: Martin Basti <mbasti@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>