commands/postgres: Upgrade the data base schema to v1.3

Upgrade the database schema to reflect the additions of directory
artifacts and the missing TargetInfo property.

wa/commands/postgres_schemas/postgres_schema_update_v1.3.sql

@@ -0,0 +1,3 @@
+ALTER TABLE targets ADD COLUMN system_id text;
+
+ALTER TABLE artifacts ADD COLUMN is_dir boolean;