IPA: Utilize new protocol in IPA extdom plugin
    
    To allow @-sign in group name IPA extdom plugin had to be
    extended. Now the protocol distinguishes between resolving
    username and groupname.
    
    Until now name resolution was performed as it is a user and
    in case of not finding any user, group search was performed.
    But the SSSD knows the type of object, that is resolved.
    
    This change will improve the performance of the system.
    
    The @-sign issue is completely fixed on IPA side and
    will work for older clients too.
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/3219
    
    Reviewed-by: Sumit Bose <sbose@redhat.com>