GRANT/REVOKE fails on the maintenance socket connections,
because maintenance_auth_service uses allow_all_authorizer.
allow_all_authorizer allows all operations, but not GRANT/REVOKE,
because they make no sense in its context.
This has been observed during PGO run failure in operations from
./pgo/conf/auth.cql file.
This patch introduces maintenance_socket_authorizer that supports
the capabilities of default_authorizer ('CassandraAuthorizer')
without needing authorization.
Refs SCYLLADB-1070
