MM-8607 Add ability to turn off non-critical services when under load (#13212)

* MM-8607: add ability to turn off non-critical services under load

* server busy invalid param unit tests

* MM-8607: rename server busy endpoints

* MM-8607: handle case where App not initialized

* MM-8607: additional unit test cases per feedback.

* MM-8607: use decorator to check isbusy when adding endpoint route

* MM-8607: rename endpoints, use struct for json

* Update api4/system.go

Fix misspelled log output

Co-Authored-By: Saturnino Abril <saturnino.abril@gmail.com>

* MM-8607: fix i18n order; max seconds for server busy expiry

wsapi/user.go

@@ -13,6 +13,11 @@ func (api *API) InitUser() {
 }
 
 func (api *API) userTyping(req *model.WebSocketRequest) (map[string]interface{}, *model.AppError) {
+	if api.App.Srv.Busy.IsBusy() {
+		// this is considered a non-critical service and will be disabled when server busy.
+		return nil, NewServerBusyWebSocketError(req.Action)
+	}
+
 	var ok bool
 	var channelId string
 	if channelId, ok = req.Data["channel_id"].(string); !ok || len(channelId) != 26 {