Lead unit missing ovn config in octavia.conf

In an OVN deployment when the configure-resources action is run the lead unit will be missing OVN configuration from its octavia.conf but the other units will have it.

This is because the lead unit renders its configuration via a call to octavia_charm.render_all_configs in the action code, whereas the other units render their config inside a hook execution. Reactive interfaces based on charms.reactive.endpoints.Endpoints are supposed to register when the hook starts *1 but this is not called in an action. So when then render is called in an action the charms.reactive.endpoints.Endpoints appear to be missing.

*1 https://github.com/juju-solutions/charms.reactive/blob/master/charms/reactive/endpoints.py#L873