iocage cannot be used with hierarchical jails #33

This is similar to iocage/iocage#1133 raised by @dlangille and inspired by https://it-notes.dragas.net/2023/11/27/migrating-from-vm-to-hierarchical-jails-freebsd/

Version: 1.8

iocage uses $pool/iocage, currently hardcoded path, to store its datasets (jails, templates, downloaded releases, etc.)

That makes it impossible to use in hierarchical (nested) jails.

I would like to have a --prefix option use to set a prefix to be used for iocage datasets, when I first activate the pool to be used, for instance: iocage activate mypool --prefix my/prefix.

Then I would expect jails to live in mypool/my/prefix/iocage/jails.

This should make it possible to use iocage within jails, like bastille: https://docs.bastillebsd.org/en/latest/chapters/zfs-support.html (see the bastille_zfs_prefix configuration directive).

Make sure to follow and check these boxes before submitting an issue! Thank you.

• Supply iocage --version
  - [ ] Supply the commands used, along with any steps to recreate it.
  - [ ] Provide the output from the command you issued.
• Supply what you expected the result or output to be
• Checked that the problem has not already been fixed on master if using
  a stable release.