Fix usage of availableIn attribute in NotificationService

The documentation says:

The availableIn attribute specifies in which types of superspaces the notification is active, it can be a comma-separated lists of types, or "*" or "all" to make the notification active in any container.

and this is correctly taken into account in NotificationService#getNotificationsForSubscriptions
But in NotificationService#addSubscriptions where we need to fix it.