SDAP: Add sdap_handle_id_collision_for_incomplete_groups()
    
    This newly added function is a helper to properly hadle group
    id-collisions when renaming incomplete groups and it does:
    - Deletes the group from sysdb
    - Adds the new incomplete group
    - Notifies the NSS responder that the entry also has to be deleted from
      the memory cache
    
    This function will be called from
    sdap_ad_save_group_membership_with_idmapping() and from
    sdap_add_incomplete_groups().
    
    Related:
    https://pagure.io/SSSD/sssd/issue/2653
    
    Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>