The ability to install unaudited extensions directly from a zip file
can be useful for testing and code review, so implement a corresponding
command that complements the previously added 'pack' command.
https://gitlab.gnome.org/GNOME/gnome-shell/issues/1234
Extensions are uploaded to extensions.gnome.org as zip files that
not only contain the extension sources, but also compiled GSettings
schemas and message catalogues. To make this more convenient, add
a corresponding command for creating an archive suitable for up-
loading.
https://gitlab.gnome.org/GNOME/gnome-shell/issues/1234