Notify master about instance status update

Send updates to the master server when the running status of instances
change and add onInstanceStatusChanged hook to master plugins.

lib/link/messages.js

@@ -535,17 +535,28 @@ messages.debugWsMessage = new Event({
 
 messages.instanceInitialized = new Event({
 	type: "instance_initialized",
-	links: ["instance-slave"],
+	links: ["instance-slave", "slave-master"],
 	eventProperties: {
+		"instance_id": { type: "integer" },
 		"plugins": {
 			type: "object",
 			additionalProperties: { type: "string" },
 		}
 	},
 });
+messages.instanceStarted = new Event({
+	type: "instance_started",
+	links: ["instance-slave", "slave-master"],
+	eventProperties: {
+		"instance_id": { type: "integer" },
+	},
+});
 messages.instanceStopped = new Event({
 	type: 'instance_stopped',
-	links: ['instance-slave'],
+	links: ["instance-slave", "slave-master"],
+	eventProperties: {
+		"instance_id": { type: "integer" },
+	},
 });
 
 messages.updateInstances = new Event({
@@ -557,9 +568,10 @@ messages.updateInstances = new Event({
 			items: {
 				type: "object",
 				additionalProperties: false,
-				required: ["serialized_config"],
+				required: ["serialized_config", "status"],
 				properties: {
 					"serialized_config": { type: "object" },
+					"status": { enum: ["stopped", "initialized", "running"] },
 				},
 			},
 		},

lib/plugin.js

@@ -163,6 +163,21 @@ class BaseMasterPlugin {
 	 */
 	async init() { }
 
+	/**
+	 * Called when the status of an instance changes
+	 *
+	 * Invoked when the master server has received notice from a slave that
+	 * the running status of an instance has changed.  The possible statuses
+	 * are `stopped` meaning it is not loaded or running, `initialized`
+	 * meaning the instance has initialized and is starting up the Factorio
+	 * server, and `running` which means the Factorio server it manages is
+	 * up and running.
+	 *
+	 * @param {Object} instance - the instance that changed.
+	 * @param {string} prev - the previous status of the instance.
+	 */
+	async onInstanceStatusChanged(instance, prev) { }
+
 	/**
 	 * Called before collecting Prometheus metrics
 	 *