Use the correct text VKey for HostResource's superordinateDomain (#608)

* Store the superordinateDomain reference as a VKey rather than Key

This is a reference to a Domain object, so we should store it as a VKey
in reference to the Domain table. This should not affect any business
logic, but rather will allow us to set up the SQL tables for
HostResource et al. properly.

db/src/main/resources/sql/schema/db-schema.sql.generated

@@ -195,7 +195,7 @@
         fully_qualified_host_name text,
         last_superordinate_change timestamptz,
         last_transfer_time timestamptz,
-        superordinate_domain bytea,
+        superordinate_domain text,
         primary key (repo_id)
     );