Service names and dns

We need to document the fact that service names get converted to kebab-case. My instinct would be to throw an error if they aren't, but I guess that's not necessarily practical.

Right now if someone has postgres_service as a service name, it gets translated into postgres-service in DNS, which makes sense, but they might not be aware of if they're used to the way docker compose works, which allows the underscores. We can do replacement for things that are visible in env in the compose file, but if someone puts that elsewhere, then it won't be automatically replaced (I can imagine a situation where someone has a dev/staging/prod config file and uses env vars to select the file for example)

The issue names no files or tests. Start by locating the documentation covering service names, DNS naming, and Docker Compose compatibility; document that service names are converted to kebab-case and explain the implications for references outside visible Compose environment values. Done means a reader can understand the conversion and its configuration-file caveat.