Ship files under /lib/modules/ rather than /boot/

In order to support the 'hermetic /usr' concept for the vendor-provided tree, we need to avoid shipping files outside of /usr/. The kernel image and related files are currently shipped in /boot/. Ship them under /lib/modules/$ver/ instead, with the same names. This also allows those wanting to use systemd-boot to follow the BLS (Boot Loader Specification https://systemd.io/BOOT_LOADER_SPECIFICATION/ ) and allow having a FAT32 /boot partition.

Copy the files from /lib/ to /boot/ on installation via a tmpfiles.d snippet. This has the advantage of allowing an easy opt-out via masking, and also allows to recreate /boot/ on factory reset/wipe if needed, without having to reinstall the package. It's also declarative, which is nice.

See: https://lists.debian.org/debian-kernel/2022/09/msg00062.html