Add some initial Sqitch migrations

These are based on the state of the current manually managed database.

sqitch/deploy/buildstatus_enum.sql

@@ -0,0 +1,18 @@
+-- Deploy guix-data-service:buildstatus_enum to pg
+-- requires: appschema
+
+BEGIN;
+
+SET client_min_messages = 'warning';
+
+CREATE TYPE guix_data_service.buildstatus AS ENUM (
+    'scheduled',
+    'started',
+    'succeeded',
+    'failed',
+    'failed-dependency',
+    'failed-other',
+    'canceled'
+);
+
+COMMIT;