RFC 629: Hydrate execution logs of `lsif_indexes`

Created by: efritz

Implements a portion of RFC 629: Cold-storing older worker execution logs.

Update GraphQL endpoints related to lsif_indexes to read execution logs from the configured sink when a forwarding address is left. Add these values to redis-cache with a bounded number of total entries.

The implementation of this change should make the caching and sink coupling as tight as possible, but they should still be completely independent from lsif_indexes. The caching strategy here should be directly usable by other consumers. A caching sink combinator seems like a good idea here (see #33033).