Tails Cloner should support Upgrade + Clone the current Persistent Storage

For the backup system that is being designed (#20194) Tails Cloner will be handling the backups. These backups are not just backups of the persistent storage, but (almost) interchangeable copies (possibly modulo size and encryption passphrase) of the source device, i.e. a ready-to-use Tails USB sticks with the same data in their persistent storage. For this reason we want to not only keep the persistent storage data up-to-date, but also the Tails that is installed on the backup device.

Tails Cloner will be used for both creating these backups and updating them, but currently we only really support creating them, which is Install + Clone the current Persistent Storage; "updating" them is the same thing, i.e. rewrite everything (which makes incremental backups (#19649) impossible), with the GUI saying "You can only choose to reinstall when cloning the Persistent Storage" and making the "Upgrade" button unavailable.

(Tails Cloner should also not upgrade Tails if it already is up-to-date, but that is #20362.)

So we need to add support for upgrading (not reinstalling) Tails when "Clone the current Persistent Storage" is checked.