feat(GODT-2801): User Service Integration

Enable the User Event, User Identity and User SMTP service. The services
don't persist any data at the moment to avoid conflict with the existing
event loop.

internal/events/events.go

@@ -35,3 +35,7 @@ func (eventBase) _isEvent() {}
 type EventPublisher interface {
 	PublishEvent(ctx context.Context, event Event)
 }
+
+type NullEventPublisher struct{}
+
+func (NullEventPublisher) PublishEvent(_ context.Context, _ Event) {}