initramfs-tools/hooks/zz-busybox: add "Adding binary-link $path" to verbose screen output

I was confused by the update-initramfs output that I got after every update. And even while running it with -v manually it didn't clear things up. The entries I got were like:

Calling hook klibc-utils
cp: not replacing '/var/tmp/mkinitramfs_F62WEu/bin/cat'
cp: not replacing '/var/tmp/mkinitramfs_F62WEu/bin/cpio'
cp: not replacing '/var/tmp/mkinitramfs_F62WEu/bin/dd'

And because currently busybox doesn't output to the screen I also couldn't see that buxybox was the reason for this error.

This hook increases the verbose screen output from currently:

Calling hook zz-busybox
Adding binary /usr/bin/busybox
Adding binary /lib/x86_64-linux-gnu/libresolv.so.2

to

Calling hook zz-busybox
Adding binary /usr/bin/busybox
Adding binary-link /var/tmp/mkinitramfs_boURK6/bin/[
Adding binary-link /var/tmp/mkinitramfs_boURK6/bin/[[
Adding binary-link /var/tmp/mkinitramfs_boURK6/sbin/acpid
Adding binary-link /var/tmp/mkinitramfs_boURK6/sbin/adjtimex
Adding binary-link /var/tmp/mkinitramfs_boURK6/bin/ar
...

which will enable our users to more easily spot such issues.

Fixing or preventing the overlap with klibc-utils is a separate task. This commit only adds the necessary debug output to allow finding such issues and probably not something for within our hook here, as /etc/initramfs-tools/initramfs.conf was set to BUSYBOX=auto I.E. according to the description If set to auto (or unset), busybox will be used if installed we should be the one installing our binaries anyway...