Make default sharded sqlite implementation asset-aware
Was going to try to do a migration of the default sqlite storage to the
ConsolidatedSqliteEventLogStorage, but then thought about this approach, which seems like it might
work and is way less complicated.
Different approaches weighed here: https://elementl.quip.com/pl6oAbOhjoUB/Asset-storage
It essentially mirrors all asset materialization events into a central assets.db sqlite file and
performs asset queries off of that db.
Test Plan: bk
Reviewers: schrockn, alangenfeld, max, sandyryza
Reviewed By: alangenfeld
Differential Revision: https://dagster.phacility.com/D5941