Run cross-release SQL integration tests (#403)

* Run cross-release SQL integration tests

Run SQL integration tests across arbitrary schema and server
releases.

Refer to integration/README.md in this change for more information.

TESTED=Cloud build changes tested with cloud-build-local
       Used the published jars to test sqlIntegration task locally.

core/src/test/java/google/registry/model/transaction/JpaTransactionManagerRule.java

@@ -85,6 +85,7 @@ public class JpaTransactionManagerRule extends ExternalResource {
   private static final String POSTGRES_DB_NAME = "postgres";
 
   // Name of the optional property that specifies the root path of the golden schema.
+  // TODO(weiminyu): revert this. The :integration project offers a better solution.
   @VisibleForTesting
   static final String GOLDEN_SCHEMA_RESOURCE_ROOT_PROP = "sql_schema_resource_root";