In some cases ActiveSession.cleanup was not called after authentication,
so for some user ActiveSession lookup keys grew without ever cleaning
up. This Rake task manually iterates over the lookup keys and removes
ones without existing ActiveSession.
This adds the rake task rake
gitlab:cleanup:orphan_job_artifact_files. This rake task cleans all
orphan job artifact files it can find on disk.
It performs a search on the complete folder of all artifacts on
disk. Then it filters out all the job artifact ID for which it could
not find a record with matching ID in the database. For these, the
file is deleted from disk.
