Experimental quiet mode

What does this Merge Request do?

This MR offers the gdk.experimental.quiet setting which currently just reduces the bundle install 'noise' by only showing when bundle install actually installs/upgrades a gem. This substantially reduces the amount of terminal output by ~85%. To test, add the following to your gdk.yml:

gdk:
  experimental:
    quiet: true

The rationale behind this change is to continue reducing what is displayed in the terminal so that important actions such as config files being updated or other calls to action are more easily spotted. This follows the UNIX philosophy of 'No news is good news' 🙂.

Merge Request checklist

• Tests added for new functionality. If not, please raise Issue to follow-up.
• This change is backward compatible. If not, please include steps to communicate to our users.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.