MM-21898 - Part 1: Generate and use an interface instead of *A… (#13840)

* Generate and use an interface instead of *App

app/email_batching.go

@@ -40,7 +40,7 @@ func (a *App) AddNotificationEmailToBatch(user *model.User, post *model.Post, te
 		return model.NewAppError("AddNotificationEmailToBatch", "api.email_batching.add_notification_email_to_batch.disabled.app_error", nil, "", http.StatusNotImplemented)
 	}
 
-	if !a.Srv.EmailBatching.Add(user, post, team) {
+	if !a.Srv().EmailBatching.Add(user, post, team) {
 		mlog.Error("Email batching job's receiving channel was full. Please increase the EmailBatchingBufferSize.")
 		return model.NewAppError("AddNotificationEmailToBatch", "api.email_batching.add_notification_email_to_batch.channel_full.app_error", nil, "", http.StatusInternalServerError)
 	}