bug#43390: eudev should have ability to add a hwdb file

[Stefan Huchler]

There is a configuration field for udev rules:

https://guix.gnu.org/manual/en/html_node/Base-Services.html
udev-service [#:udev eudev #:rules '()]

But there is no configuration option to add a hwdb file.

I don't know if that matters but nixos has such option:
services.udev.extraHwdb

That's the hwdb file I want to add:
https://github.com/spiderbit/emacs-ergo-thinkpad-kb-layout/archive/master.zip