## Problem
We had a recent Postgres startup latency (`start_postgres_ms`)
degradation, but it was only caught with SLO alerts. There was actually
an existing test for the same purpose -- `start_postgres_ms`, but it's
doing only two starts, so it's a bit noisy.
## Summary of changes
Add new compute startup latency test that does 100 iterations and
reports p50, p90 and p99 latencies.
Part of https://github.com/neondatabase/cloud/issues/24882
