pkg/conf: deadlock detector: clarify prod error messages + use lenient timeout

Created by: slimsag

pkg/conf has logic to detect deadlocks where someone relies on configuration in the frontend and inadvertently prevents the frontend configuration server from starting (hence, a deadlock).

In some cases where PostgreSQL takes very long to startup this logic can trigger, thus we should only do so aggressively in dev mode. However, it is still useful in prod so that we can debug any other case where the frontend config server is blocked from starting for a very long period of time.

Fixes #2812

Test plan: not necessary (making logic more lenient)