openstack: networking-ovn-metadata-agent configuration not re-rendered on charm upgrade

The configuration for ``networking-ovn-metadata-agent`` is currently not re-rendered on charm upgrade.

This is due to the reconfiguration of OVS being guarded behind certificate changes, probably as a side effect of the calls ``configure_ovs`` make to OVS may hang when already configured and that the method restarts daemons at the end.

We should make the ``configure_ovs`` method compare run-time configuration prior to making calls to OVS and make the call to restart daemons happen only when strictly necessary.