Now that the bcachefs tool unconditionally includes the mount parts
(or more correctly, you cannot build it at all if you don't have Rust),
we can call copy_exec on mount.bcachefs, to get the symlink installed.
In particular, this helps with mounting UUID mounts as /.
See also https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1060411
for the remaining parts needed in initramfs-tools itself.
thie enables building it in a different directory, more
flexible install and configure options, and should make it
easier to eventualy create deb and rpm packages. Additionally
this makes it much easier to build and test this package
as it now behaves the same way as others we are using.
This means bcache devices will be registered earlier and in all
cases, not just when the rootfs fails to mount.
The initramfs hook is still there to ensure the bcache module
and udev rules are shipped if an initramfs is used.
