A few minor changes to get #119638 - nextcloud: add option to set
datadir and extensions - ready:
* `cfg.datadir` now gets `cfg.home` as default to make the type
non-nullable.
* Enhanced the `basic` test to check the behavior with a custom datadir
that's not `/var/lib/nextcloud`.
* Fix hashes for apps in option example.
* Simplify if/else for `appstoreenable` in override config.
* Simplify a few `mapAttrsToList`-expressions in
`nextcloud-setup.service`.
Note the appstoreEnable which will prevent nextcloud form updating
nix-managed apps. This is needed because nextcloud will store an other
version of the app in /var/lib/nextcloud/store-apps and it will
no longer be manageable.
