Allow doing a backup of the Persistent Storage when cloning

We already have a design on the blueprint (https://tails.boum.org/blueprint/backups) so there's not much UX work left to do.

Or we do it the other way around with #18757 (closed).

Doc update:

Update "Create a new Tails to store your backup" to use Tails Installer
Change "Create or update your backup" to be "Update your backup using the graphical utility"

Edited Jun 08, 2023 by sajolida

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