WARC Server occasionally 'forgetting' WARCs

[anjackson]

Just had an issue where warc-server seemed to loose track of some WARCs leading to playback problems. This was resolved by restarting it, but there's clearly some underlying issue. Would be good to revisit this and see if there's a more robust approach.

Current model queries TrackDB and stores the resulting map in memory. This is a bit clumsy, and means if TrackDB happens to be down when the service restarts, playback will break.

A more robust approach would be to emit/update something like a SQLite database. An Airflow task could update it independently, and the WARC server could look things up in it as a read-only client.