Bump the size of the system partition created by Tails Installer

This is about:

• creating a bigger system partition, whose size depends on the size of the target device;
• handling nicely the fact that “Clone and Upgrade” will become impossible in some cases;
• refusing installing a new Tails on a device smaller than 8 GiB.

See the parent ticket for detailed specifications, and see #11627 (closed) for UI messages that sajolida drafted already (I expect they’ll be worked on again but that should be enough to get started with the coding).

Feature Branch: feature/12705-bump-system-partition-size, installer:feature/12705-bump-system-partition-size

Parent Task: #12705 (closed)

Related issues

• Blocks #13234 (closed)

Original created by @intrigeri on 12707 (Redmine)