Replace logs.minEntry with a call to get-sth on first run

[Preston12321]

When monitoring large, rapidly-growing logs, it becomes unwieldy to keep the minEntry config field up to date with the STH. This means that clean redeploys often result in the inclusion checker reporting unincorporated certs when, in fact, the checker simply hasn't caught up to the location in the log where its test certs were submitted. A delay of even a few days between updating the config with the then-current tree size of a log like Oak 2024h2 and re-deploying ct-woodpecker can cause this issue.

I think we should remove the minEntry field entirely, and instead use the tree size reported by get-sth to seed the StartIndex for each log's inclusion checker. This would only happen when there isn't already a non-zero index value in the database for the log, so that subsequent restarts of woodpecker don't cause the inclusion checker to jump ahead unintentionally.