[bug#60521] [PATCH] home: Add home-stow-migration-service.

[goodoldpaul]

Dear Guixers,

I'm upstreaming a Guix Home service I've been using for quite some time 
in my personal channel ( 
https://gitlab.com/orang3/small-guix/-/blob/master/small-guix/home/services/dotfiles.scm 
) with some small improvements to make it suitable for Guix mainline.

The point of this service is to allow GNU Stow users to switch to Guix 
Home without any change to their Stow directory structure, in the hope 
of easing the way into Guix Home allowing users to avoid convert all of 
their dotfiles to Guix native configurations.

Thank you for your time and efforts,

giacomo