POC boot kernel from data partition

[ycardaillac]

Try to avoid duplicating the boot dir (kernel + init) by booting it from data partition

Works only with Grub now.

https://balena.fibery.io/Work/Project/Deduplicate-kernel-on-balenaOS-rootfs-2300

Change-type: major

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[flowzone-app]

Website deployed to CF Pages, 👀 preview link https://ba8a5154.balena-os.pages.dev