Debugging gitaly with gitaly-debug

In GitLab 11.6 and up, Gitaly comes with a debugging tool gitaly-debug that can be run on a production Gitaly server. It is meant to avoid having to copy-paste shell scripts when troubleshooting. For a list of its current abilities, see the gitaly-debug README.

As of 11.6 the only feature of gitaly-debug is to simulate the server-side workload of a Git clone on a specific repo. We hope to add more tools over time.