MM-24830: Add event constants for gossip request/response (#14611)

* MM-24830: Add event constants for gossip request/response

This is an accompanying PR for the shift to entirely gossip.

* Fix order

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

model/cluster_message.go

@@ -43,6 +43,16 @@ const (
 	CLUSTER_EVENT_INVALIDATE_CACHE_FOR_TERMS_OF_SERVICE             = "inv_terms_of_service"
 	CLUSTER_EVENT_BUSY_STATE_CHANGED                                = "busy_state_change"
 
+	// Gossip communication
+	CLUSTER_GOSSIP_EVENT_REQUEST_GET_LOGS             = "gossip_request_get_logs"
+	CLUSTER_GOSSIP_EVENT_RESPONSE_GET_LOGS            = "gossip_response_get_logs"
+	CLUSTER_GOSSIP_EVENT_REQUEST_GET_CLUSTER_STATS    = "gossip_request_cluster_stats"
+	CLUSTER_GOSSIP_EVENT_RESPONSE_GET_CLUSTER_STATS   = "gossip_response_cluster_stats"
+	CLUSTER_GOSSIP_EVENT_REQUEST_GET_PLUGIN_STATUSES  = "gossip_request_plugin_statuses"
+	CLUSTER_GOSSIP_EVENT_RESPONSE_GET_PLUGIN_STATUSES = "gossip_response_plugin_statuses"
+	CLUSTER_GOSSIP_EVENT_REQUEST_SAVE_CONFIG          = "gossip_request_save_config"
+	CLUSTER_GOSSIP_EVENT_RESPONSE_SAVE_CONFIG         = "gossip_response_save_config"
+
 	// SendTypes for ClusterMessage.
 	CLUSTER_SEND_BEST_EFFORT = "best_effort"
 	CLUSTER_SEND_RELIABLE    = "reliable"