Add new derivation_output_details_set_id column to the builds table

As this will hopefully provide a faster way of associating derivations with
builds.

sqitch/revert/builds_add_derivation_output_details_set_id.sql

@@ -0,0 +1,7 @@
+-- Revert guix-data-service:builds_add_derivation_output_details_set_id from pg
+
+BEGIN;
+
+-- XXX Add DDLs here.
+
+COMMIT;