[bug#73927] [PATCH 16/16] DRAFT installer: Support dry-run from Guile via store.

[Mathieu Othacehe]

Hello,

> This supports running the installer quasi-directly from Guile by only building
> a Guile installer-script in the store.  Do something like:
>
>     ./pre-inst-env guile -c '((@ (gnu installer) run-installer) #:dry-run? 
> #t)'
>
>     sudo -E ./pre-inst-env guile -c '((@ (gnu installer) run-installer))'

I remember resorting to a similar hack, back in 2018 when writing the
installer. Maybe we should go the extra mile and integrate that one to a
proper guix command, such as `guix system installer` that would call
`run-installer` with dry-run set to #t. WDYT?

Thanks,

Mathieu