codeintel: RFC 235: Update bundle manager to read from Postgres
Created by: efritz
A step towards RFC 235: Move LSIF data to Postgres. Closes https://github.com/sourcegraph/sourcegraph/issues/13886.
This PR adds a db call to the new Postgres-backed bundle store introduced https://github.com/sourcegraph/sourcegraph/pull/13923 before falling back to disk. Do not merge this PR until https://github.com/sourcegraph/sourcegraph/issues/13883 and https://github.com/sourcegraph/sourcegraph/pull/13903 has been completed and deployed.