Add a generic artifact builder based on a provided Dockerfile.

In this MR we introduce scripts that allow a project to:

1. Use a Dockerfile to manage their own build.
2. Specify the final artifact that (1) generates. No assumptions of the artifact type are made.
3. Publish such artifact in the calling projects' package registry.

These build scripts deprecate the need to copy and paste a Dockerfile onto a gitlab CI script. Once merged we could remove scripts related to !28 (merged).

Since the scripts invoke the docker command, the assumption is that the gitlab runner has access to docker. See comment thread on https://phabricator.wikimedia.org/T321736 for how we have built such a runner.