codeintel: RFC 235: Create connection to codeintel database
Created by: efritz
Steps toward RFC 235: Move LSIF data to Postgres. Closes https://github.com/sourcegraph/sourcegraph/issues/13884.
This PR adds CodeIntelPostgresDSN
to conftypes and connects to the configured DSN in the bundle manager and the worker. Do not merge this PR until https://github.com/sourcegraph/sourcegraph/issues/13883 has been completed and deployed.