ALTER ROLE ----> <role-name> --+----------------------+------>
                                 +--> alter-role-opts --+

  alter-role-opts =

  --+--> IDENTIFIED EXTERNALLY -------------+---->
    +--> NOT IDENTIFIED --------------------+
    +--> RENAME TO <new-role-name> ---------+
    +--> COMMENT IS --+--> 'string' --+-----+
                      +--<--- / ------+