Create preflight check for all pre-reqs

Add a preflight check to verify prereqs and proper versions are setup: https://gitlab.com/gitlab-org/gitlab-development-kit/blob/master/doc/prepare.md

Created as apart of breaking down #594 (closed)

1. ruby was using v2.4.4, not v2.6.3, for some reason, so one of the startup Ruby scripts died because it was using 2.6.3 syntax. I didn't see a .ruby-version in the GDK dir though. I had to force a rvm use 2.6.3 to get this to work. Perhaps we need to do a version check to make sure it's set up properly.

• Ruby
• Go
• Git
• Bundler
• Node
• Yarn