codeintel: Publish index configuration from database
Created by: efritz
This PR adds a table to the frontend Postgres instance that stores a configuration payload for index-configured repositories. We don't currently have a way to insert these records (so manual db access OR additional work on the UI/GraphQL API will be required to insert records for https://github.com/sourcegraph/sourcegraph/issues/14343).
This closes https://github.com/sourcegraph/sourcegraph/issues/14409.