MM-34878: Add metrics for websocket reconnects (#17522)

* MM-34878: Add metrics for websocket reconnects

Added two new metrics to track successful websocket drain
and dead queue misses.

```release-note
NONE
```

https://mattermost.atlassian.net/browse/MM-34878

* remove TODO line

einterfaces/metrics.go

@@ -43,6 +43,7 @@ type MetricsInterface interface {
 	DecrementWebSocketBroadcastBufferSize(hub string, amount float64)
 	IncrementWebSocketBroadcastUsersRegistered(hub string, amount float64)
 	DecrementWebSocketBroadcastUsersRegistered(hub string, amount float64)
+	IncrementWebsocketReconnectEvent(eventType string)
 
 	AddMemCacheHitCounter(cacheName string, amount float64)
 	AddMemCacheMissCounter(cacheName string, amount float64)

einterfaces/mocks/MetricsInterface.go

@@ -230,6 +230,11 @@ func (_m *MetricsInterface) IncrementWebsocketEvent(eventType string) {
 	_m.Called(eventType)
 }
 
+// IncrementWebsocketReconnectEvent provides a mock function with given fields: eventType
+func (_m *MetricsInterface) IncrementWebsocketReconnectEvent(eventType string) {
+	_m.Called(eventType)
+}
+
 // ObserveApiEndpointDuration provides a mock function with given fields: endpoint, method, statusCode, elapsed
 func (_m *MetricsInterface) ObserveApiEndpointDuration(endpoint string, method string, statusCode string, elapsed float64) {
 	_m.Called(endpoint, method, statusCode, elapsed)