Geo: Add easy installation script

What does this Merge Request do and why?

Make it easy to go from 0 GDKs to 2 GDKs with Geo configured properly.

If you have no GDK yet: How to easy install 2 GDKs and configure Geo

export GITLAB_LICENSE_KEY=$(cat /path/to/your/premium.gitlab-license)
curl "https://gitlab.com/gitlab-org/gitlab-development-kit/-/raw/mk/easy-install-geo/support/geo-install" | bash -s gdk gdk2 mk/easy-install-geo

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• [-] Tests added for new functionality. If not, please raise Issue to follow-up. => #1233 (closed)
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.