Add a property in Registry to disable invoicing (#644)

The added property will by default be null for existing entities and false for new entities. We could write a temporary MapReduce to set it to false for all existing ones, but it seems easier to just modify the query to account for the nullness of the column. The need to check for null won't exist once we migrate the Registry entity to Cloud SQL.

TESTED=deployed to alpha, set the property for tld zombo to true and triggered an export, verified that the column is null for all rows other than the row for zombo.

core/src/test/resources/google/registry/beam/invoicing/billing_events_test.sql

@@ -56,7 +56,8 @@ FROM (
       `my-project-id.latest_datastore_export.Registry`
     WHERE
     -- TODO(b/18092292): Add a filter for tldState (not PDT/PREDELEGATION)
-      tldType = 'REAL') ) AS BillingEvent
+      tldType = 'REAL'
+    AND disableInvoicing is not TRUE) ) AS BillingEvent
   -- Gather billing ID from registrar table
   -- This is a 'JOIN' as opposed to 'LEFT JOIN' to filter out
   -- non-billable registrars

core/src/test/resources/google/registry/model/schema.txt

@@ -494,6 +494,7 @@ enum google.registry.model.registrar.RegistrarContact$Type {
 class google.registry.model.registry.Registry {
   @Id java.lang.String tldStrId;
   @Parent com.googlecode.objectify.Key<google.registry.model.common.EntityGroupRoot> parent;
+  boolean disableInvoicing;
   boolean dnsPaused;
   boolean escrowEnabled;
   com.googlecode.objectify.Key<google.registry.model.registry.label.PremiumList> premiumList;