Set default attachtment folder to "/Apps/Deck"

[joeschi]

Many apps create an attachment folder. This becomes confusing for users because it unnecessarily inflates their folder structure.

So why not a common basis for default attachment folders: “/Apps”?

As a result, all apps folders are then grouped together under “Apps”: /Apps/Deck, /Apps/Forms, /Apps/Calendar, /Apps/Talk, etc.

I have also opened an issue in Talk nextcloud/spreed#14706

[nickvergessen]

Duplicate of nextcloud/server#46309