proposal: appview atproto reconciler #306

There are several fake records that exist in appview db but not in PDS. We need a way to easily identify those and remove/restore them.

to identify fake records & cleanup them from appview, run a reconciler service in background.

This service will

1. iterate over all known records
2. check if same record exists in upstream PDS by comparing CID.

related:

• #387 - proposal: prefer com.atproto.repo.strongRef over at-uri
• #405 - proposal: move db logic to ingester