bug#44353: [PATCH version-1.2.0 v2] guix: system: Add a new '--non-volatile' option for disk-image.

[Mathieu Othacehe]

Hello Maxim,

> * guix/scripts/system.scm (%options)[volatile-root?]: New boolean option.
> (%default-options): Set its default value to #f.
> (show-help): Add help doc.
> * guix/scripts/system.scm (perform-action): Propagate option...
> (system-derivation-for-action): ...here.  Use it to set the volatile-root?
> field of the image object passed to SYSTEM-IMAGE.
> * doc/guix.texi (Invoking guix system): Document it.

This is a nice addition and it looks good to me.

Thanks,

Mathieu