Finalize the config "local" deprecation in favor of "postgresql"
This will remove further deprecation warnings from the tests, especially the ones from other modules depending on the storage's pytest-plugin.
This also fixes some edge case configuration for the backfill and the storage rpc backend which would have been broken if we switched to that new name prior to this.
Related to b487a21f
Test Plan
tox
Migrated from D5763 (view on Phabricator)