iocage cannot be used with hierarchical jails

[Defenso-QTH]

This is similar to https://github.com/iocage/iocage/issues/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).

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• [x] Supply iocage --version - [ ] Supply the commands used, along with any steps to recreate it. - [ ] Provide the output from the command you issued.
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[Defenso-QTH]

I provided a draft PR to address this but there is still an issue to address, please join the discussion!