[+] add function GetSubscriberByUser for the agenda-widget

storage/mongodb.go

@@ -153,3 +153,11 @@ func (s MongoDBStorage) UpdateEvent(event Event) error {
 
 	return nil
 }
+
+func (psql MongoDBStorage) GetSubscriber(subscriber string) ([]Subscription, error) {
+	return nil, nil
+}
+
+func (psql MongoDBStorage) GetSubscriptionByUser(subscriber string) ([]Subscription, error) {
+	return nil, nil
+}