[bug#46031] services: cuirass: Add "simple-cuirass-services".

[Mathieu Othacehe <othacehe@gnu.org>]

Hey Ludo!

> I had overlooked these patches; that’s really nice!

Thanks :)

> I wonder if it would make sense to allow users to pass directly a
> manifest, as in (pseudo syntax):
>
>   (simple-cuirass-configuration
>     (build (list (build-manifest … (local-file "my-manifest.scm"))))
>     (channels …))

It would be nice but Cuirass doesn't support specification update for
now. Passing a manifest this way would require to drop the database
content at each reconfiguration.

> What about exposing ‘simple-cuirass-configuration->specs’, and document
> it such that one can do:
>
>   (service cuirass-service-type
>            (cuirass-configuration
>              (specifications
>               (simple-cuirass-configuration->specs config))))

I agree it feels nicer, however with this service I'd like to hide the
dependencies to postgresql-service-type and
postgresql-role-service-type. That's why "simple-cuirass-services"
returns three services. Maybe you see another way?

Thanks,

Mathieu