[MM-16667] Migrate User.GetByUsername to Sync by default #11453 (#11520)

* Migrate User.GetByUsername to Sync by default #11453

* fix app errors #11453

* fix app errors #11453

* fix cmd error #11453

* fix shadow var #11453

* fix shadow user var #11453

* fix test error

* fix test error #11453

app/webhook.go

@@ -589,10 +589,10 @@ func (a *App) HandleIncomingWebhook(hookId string, req *model.IncomingWebhookReq
 
 	if len(channelName) != 0 {
 		if channelName[0] == '@' {
-			if result := <-a.Srv.Store.User().GetByUsername(channelName[1:]); result.Err != nil {
-				return model.NewAppError("HandleIncomingWebhook", "web.incoming_webhook.user.app_error", nil, "err="+result.Err.Message, http.StatusBadRequest)
+			if result, err := a.Srv.Store.User().GetByUsername(channelName[1:]); err != nil {
+				return model.NewAppError("HandleIncomingWebhook", "web.incoming_webhook.user.app_error", nil, "err="+err.Message, http.StatusBadRequest)
 			} else {
-				if ch, err := a.GetOrCreateDirectChannel(hook.UserId, result.Data.(*model.User).Id); err != nil {
+				if ch, err := a.GetOrCreateDirectChannel(hook.UserId, result.Id); err != nil {
 					return err
 				} else {
 					channel = ch