Abort boot when any live-config hook fails

Currently, if any of our live-config hooks fail, Tails still boots without reporting an error (at least not in a way that’s obvious to the user), and without running any of the subsequent live-hooks and we get stuff like #9149 (closed). We should instead abort booting + writing an appropriate error message. It’s also worth considering to allow continue the boot process (without aborting subsequent live-config hooks) upon user confirmation.

Unfortunately I believe achieving any of the above will require modifying live-config. Perhaps there are other reasons to start using something else, like making them into systemd unit files?

Related issues

• Related to #9149 (closed)
• Related to #6766

Original created by @anonym on 9234 (Redmine)