Summary
This is motivated by #34776 (comment) and a follow-up to #34776.
The motivation is that when a user runs contrib/guix/guix-clean it will clean the whole directory or nothing leading the user to have to manually clear out these files. It would be useful to be able to exclude certain files.
It adds the --exclude and --help/-h parameters to contrib/guix/guix-clean
Right now, when a user runs that script, it will delete everything. It makes sense to allow the user to exclude any files or directories from being removed.