worker: Migrate codeintel janitor
Created by: efritz
This PR moves the background jobs that clean up stale/reconcile remote code intel data from the frontend. Fixes https://github.com/sourcegraph/sourcegraph/issues/21762. Partial fix to https://github.com/sourcegraph/sourcegraph/issues/18253.
This is the first set of jobs being put into the worker, and docs and additional observability efforts will follow shortly after we ensure that this runs in dogfood and cloud clusters properly.