Grow system partition during boot when started from USB

Currently, Tails Installer creates a system partition if size 4 GiB or 8 GiB during installation. It would vastly increase the size of the USB image if we would include such a big partition in it, and unnecessarily so, because the partition is mostly empty. The plan is to instead ship a USB image of minimum size, and increase the size of the system partition during the first boot of the device.

Feature Branch: feature/15292-repartition

Parent Task: #15293 (closed)

Related issues

Related to #15681 (closed)
Related to #15987 (closed)
Blocks #16003 (closed)

Original created by @segfault on 15319 (Redmine)

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