Move labels out of the bootloader interface, while moving copying assets into the bootloader interface. GRUB is using one set of assets, `sd-boot` will be using another one. Fix the problem with `bootloader.Probe()` finding boot partition on the host when it runs in a priv container, fixing issues with image creation in the CI. Signed-off-by: Andrey Smirnov <andrey.smirnov@talos-systems.com>