[MM-35077] Add basic support for plugin intra-cluster communication (#17495)

* Add basic support for plugin intra-cluster communication

* Some renaming for added clarity

* Allow sending cluster event to specific nodes

* Improve naming and documentation

* Improve logging

model/cluster_message.go

@@ -40,6 +40,7 @@ const (
 	CLUSTER_EVENT_CLEAR_SESSION_CACHE_FOR_ALL_USERS                 = "inv_all_user_sessions"
 	CLUSTER_EVENT_INSTALL_PLUGIN                                    = "install_plugin"
 	CLUSTER_EVENT_REMOVE_PLUGIN                                     = "remove_plugin"
+	CLUSTER_EVENT_PLUGIN_EVENT                                      = "plugin_event"
 	CLUSTER_EVENT_INVALIDATE_CACHE_FOR_TERMS_OF_SERVICE             = "inv_terms_of_service"
 	CLUSTER_EVENT_BUSY_STATE_CHANGED                                = "busy_state_change"