Curate list of Stackspin-included Nextcloud apps

Recently we learned that although we installed the groupfolders nextcloud app, it could not be enabled in Stackspin 2.6 because the app version was not compatible with the nextcloud version (25): #1552 (closed). We fixed that particular case by upgrading nextcloud to 26.

However, this can easily happen again. For example, renovatebot has already proposed to upgrade groupfolders again which would make it once again incompatible.

To prevent this from happening, we should maybe enable all apps that we install by default so we'll enable them in our CI runs. Now that it's easier to add nextcloud apps to individual clusters, maybe some of the apps can also be removed from the default set.