Enable qos extension_driver in ovn_db_sync

In Change Ib597b62017b56b41009dd4d7359e169f424272b0, the 'qos'
service_plugin is enabled when doing an ovn_db_sync. However, if the
'qos' extension_driver is not installed, it will error out.

Append 'qos' extension_driver when using sync to fix this issue.

Closes-Bug: #1988577
Change-Id: I422d86b8e5650ced4e2cc722cea9cc30061905b4

Author: waipeng

neutron/cmd/ovn/neutron_ovn_db_sync_util.py

@@ -203,6 +203,9 @@ def main():
             'port_forwarding',
             'qos'
         ]
+        extension_drivers = list(set(cfg.CONF.ml2.extension_drivers + ['qos']))
+        cfg.CONF.set_override('extension_drivers', extension_drivers, 'ml2')
+
     else:
         LOG.error('Invalid core plugin : ["%s"].', cfg.CONF.core_plugin)
         return