Add 'tools' build image to operator codebase
As discussed in gitlab-org/gitlab-build-images!422 (comment 635740300) we should look into co-hosting gitlab-operator
code along with "build image" code that we use to shorten the loop on development and release of newer operator that may require changes to the "build image"
This is a "destination" issue. Source issue is gitlab-org/gitlab-build-images#86