Add SQL schema additions for DatabaseMigrationStateSchedule (#1274)

db/src/main/resources/sql/flyway/V100__database_migration_schedule.sql

@@ -0,0 +1,22 @@
+-- Copyright 2021 The Nomulus Authors. All Rights Reserved.
+--
+-- Licensed under the Apache License, Version 2.0 (the "License");
+-- you may not use this file except in compliance with the License.
+-- You may obtain a copy of the License at
+--
+--     http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+
+CREATE TABLE "DatabaseMigrationStateSchedule" (
+   id int8 NOT NULL,
+   migration_transitions hstore,
+   PRIMARY KEY (id)
+);
+
+CREATE UNIQUE INDEX database_migration_state_schedule_singleton
+   ON "DatabaseMigrationStateSchedule" ((true));