Use composite primary key for HostHistory and ContactHistory (#809)

* Use composite primary key for HostHistory and ContactHistory

* Update flyway file version

* Make getters private

* Add javadoc

* Rebase on HEAD

db/src/main/resources/sql/flyway/V59__use_composite_primary_key_for_contact_and_host_history_table.sql

@@ -0,0 +1,23 @@
+-- Copyright 2020 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.
+
+alter table "ContactHistory" drop constraint "ContactHistory_pkey";
+
+alter table "ContactHistory"
+    add constraint "ContactHistory_pkey" primary key (contact_repo_id, history_revision_id);
+
+alter table "HostHistory" drop constraint "HostHistory_pkey";
+
+alter table "HostHistory"
+    add constraint "HostHistory_pkey" primary key (host_repo_id, history_revision_id);