[MM-64244] Add websocket disconnect reason metric (#31032)

We've recently spent some effort improving websocket reconnection logic. With this commit, I've augmented the websocket reconnect metric to include a disconnect reason. This will help us measure the impact of these changes in production.

server/enterprise/metrics/metrics.go

@@ -726,7 +726,7 @@ func New(ps *platform.PlatformService, driver, dataSource string) *MetricsInterf
 			Help:        "Total number of websocket reconnect attempts",
 			ConstLabels: additionalLabels,
 		},
-		[]string{"type"},
+		[]string{"type", "disconnect_err_code"},
 	)
 	m.Registry.MustRegister(m.WebSocketReconnectCounter)
 
@@ -1822,8 +1822,14 @@ func (mi *MetricsInterfaceImpl) IncrementWebsocketEvent(eventType model.Websocke
 	mi.WebsocketEventCounters.With(prometheus.Labels{"type": string(eventType)}).Inc()
 }
 
-func (mi *MetricsInterfaceImpl) IncrementWebsocketReconnectEvent(eventType string) {
-	mi.WebSocketReconnectCounter.With(prometheus.Labels{"type": eventType}).Inc()
+func (mi *MetricsInterfaceImpl) IncrementWebsocketReconnectEventWithDisconnectErrCode(eventType string, disconnectErrCode string) {
+	if disconnectErrCode == "" {
+		disconnectErrCode = "unknown"
+	}
+	mi.WebSocketReconnectCounter.With(prometheus.Labels{
+		"type":                eventType,
+		"disconnect_err_code": disconnectErrCode,
+	}).Inc()
 }
 
 func (mi *MetricsInterfaceImpl) IncrementWebSocketBroadcastBufferSize(hub string, amount float64) {