Allow Encryption of ix-apps

Also, I’ve unintentionally made an encrypted version of ix-apps on a system by using zfs send/receive with the -x encryption flag to migrate into an newly encrypted pool (which makes any received datasets inherit encryption de-facto.)

This was done on 24.10 and survived the update to 25.04 fine, the only side-effect I can see is that there are a bunch of newly made datasets in ix-apps/app_mounts that still get created unencrypted. these are all for the catalogue apps using host-paths so they are all empty, incidentally enough.

the dataset is inheriting encryption from the main pool, automatically unlocked.

NAME             PROPERTY    VALUE        SOURCE
Reality/ix-apps  encryption  aes-256-gcm  -

however some datasets in app_mounts are not…

NAME                                              PROPERTY    VALUE        SOURCE
Reality/ix-apps/app_mounts/wordpress/mariadbData  encryption  off          default

Even though the dataset is empty (the app is and always has been using host-path for the database)

NAME                                               USED  AVAIL  REFER  MOUNTPOINT
Reality/ix-apps/app_mounts/wordpress/mariadbData    96K  2.38T    96K  /mnt/.ix-apps/app_mounts/wordpress/mariadbData