This change also starts passing in the manifest interface, rather than the raw data, to the model for writing.
Note that this change does *not* backfill the existing rows in to the new tables; that will occur in a followup PR. The new columns in `tagmanifest` and `tagmanifestlabel` will be used to track the backfill, as it will occur in a worker.
While this means we need an additional query for initial lookup, it makes the *filtering* query (which is the heavy part) require far fewer joins, thus making it more efficient.
Also adds a new unit test to verify that our filter filters to the correct set of repositories.
