docker compose debug instrumentation

Created by: keegancsmith

For Sourcegraph single image and Kubernetes we have debug instrumentation. This is where we forward to the private debug port on a service to expose tracing/pprof/debug interfaces/etc. This doesn't currently work for docker-compose deployments.

This codes strongest owner is distribution. However, it was based off code originally written for search (pkg/endpoint). Additionally it feels like a proper service registry/discovery would be useful for multiple environments and feels a bit like core application :) For now I am on the core search support rotation, and this would of been useful. So I am gonna add it to my worklog this week for if I have time to tackle it.