RFC: move kernels out of /boot

Some distributions have started to move the kernels out of the boot directory by default and let the install hooks etc handle copying them over.

The kernel hooks would then copy the kernels into /boot, users could then change the hooks to i.e. allow to create unified kernel image (UKI) executable without the extra duplication between the UKI file and the package dropped kernel binary.

Seems like the "standard" location for kernel files would be /usr/lib/modules/${VERSION}/vmlinuz.

Advantages:

• kernels can be copied to /boot and modified for i.e. signing.
• kernels don't have to be copied to /boot for UKIs.
• kernel.d post install moves kernels after the initramfs hook, the stupid grub mkconfig wouldn't pick up kernels for which initramfs generation failed. (https://github.com/void-linux/void-packages/issues/46006)
• Maybe good for raspberrypi kernels too, let install hooks move them to the weird kernel8.img names?

Start by tracing the kernel hooks, kernel.d post-install handling, and the initramfs hook that currently place kernels in /boot. Review how grub mkconfig discovers kernels and compare that flow with storing them under /usr/lib/modules/${VERSION}/vmlinuz. Done would require an agreed implementation for hook-managed copying, signing, UKIs, and Raspberry Pi kernel names.