bug#71571: guix-home-service-type does not create new home generations

[Richard Sent]

Hi Guix.

This is a continuation of a previous discussion [1]. I'm opening a
standalone bug to try and track it better.

At present, when guix-home-service-type is used, new home generations
are never created/registered. This causes commands that operate on
home-generations to return inaccurate or garbage information. For
instance, guix home describe -I will not report the current list of
installed packages.

Defining the interactions between guix-home-service-type and various
guix home subcommands is challenging. The proper behavior is not always
obvious [1]. Per a followup from Ludo [2], a good starting point is for
a new home generation to be created when activating a new system while
using guix-home-service-type.

[1]: https://issues.guix.gnu.org/69781#5
[2]: https://issues.guix.gnu.org/69781#6-lineno22

-- 
Take it easy,
Richard Sent
Making my computer weirder one commit at a time.