Allow database queue pool max overflow to be set in config.

For the sync workload we really want a small pool size and a large max
overflow, but in any case it makes sense for both parameters to be tunable.
Refresh ES index after recreation so tests pass with repeated creation/deletion.
Test bulk indexing.
New indexer - wip.
As a service.
Fixes for index_id, object_repr stored.
TODO: Handle deletes.
Handle deletes.
TODO:
1. Verify updates work as is.
2. Persist txn. ptr.
Fix updates.
SearchIndexService test.
Persist txn. ptr to support restarts.