LDAP: Turn group request into user request for MPG domains if needed
    
    If the primary group GID or the group name is requested before the user
    is, we need to also search the user space to save the user in the back
    end which then allows the responder to generate the group from the
    user entry.
    
    Related:
        https://pagure.io/SSSD/sssd/issue/1872
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>