Move /etc/default/grub to /etc/grub as it's owned by the sysadmin.
Move /etc/grub.d to /etc/default/grub.d as it's owned by the system.
Support /etc/grub's GRUB_CMDLINE_SORTIX in 10_sortix.
Remove the old /etc/grub.d/10_sortix.cache with a compatibility hook as it
has moved to /etc/default/grub.d/10_sortix.cache.
The custom initrd format was originally useful when it was mounted,
however it has been extracted into the ramfs for a very long time and
has no advantages over the standard tar format which can be readily
created and modified using standard tools. The kernel initrd(7) support
already supports tar, so this change simply switches the format.
Jonas 'Sortie' Termansen