In-place airgap Flatcar upgrade

[Frostman]

We need to be able to apply Flatcar upgrades automatically when upgrading the Control Node(s). It's mandatory to support it in a fully air-gapped way (we need to ship the updater with the installer/updater).

Flatcar docs on how to apply the upgrade in offline mode: https://www.flatcar.org/docs/latest/setup/releases/update-strategies/#airgapped-updates

• test that applying the Flatcar upgrade doesn't break anything on the control node (before and after the reboot)
• copy flatcar upgrade bin to our ghcr.io
• add flatcar upgrade bin to the installer artifacts
• automatically apply flatcar upgrade bin (it should be conditional - check current version and do the reboot if required)

[Frostman]

it should become part of the hhfab-recipe control upgrade, probably just in the end of it after the prompt for the users

[Frostman]

https://github.com/githedgehog/fabricator/blob/master/pkg/fab/recipe/control_upgrade.go#L166-L168

[cesargithedgehog]

Manual tests on the upgrade:

core@control-1 ~ $ sudo flatcar-update --to-version 4186.0.0 --to-payload flatcar_production_update.gz

Before upgrading:
core@control-1 ~ $ uname -a Linux control-1 6.6.60-flatcar #1 SMP PREEMPT_DYNAMIC Tue Nov 12 16:20:46 -00 2024 x86_64 Intel(R) Core(TM) Ultra 7 165U GenuineIntel GNU/Linux

After upgrading:
core@control-1 ~ $ uname -a Linux control-1 6.6.65-flatcar #1 SMP PREEMPT_DYNAMIC Fri Dec 13 11:52:04 -00 2024 x86_64 Intel(R) Core(TM) Ultra 7 165U GenuineIntel GNU/Linux

• https://update.release.flatcar-linux.net/amd64-usr/

[cesargithedgehog]

Flatcar upgrade bin - ghcr.io:

• docker pull ghcr.io/githedgehog/fabricator/flatcar-update:v4081.2.0

[cesargithedgehog]

add flatcar upgrade bin to the installer artifacts - #369