Add indexes to DomainHistory sub tables (#1319)

* Add indexes to DomainHistory sub tables

Add indexes to DomainTransactionRecord and DomainDsDataHistory to speed
up query for DomainHistory. Without these indexes, DomainHistory loading
is extremely slow: 2 QPS with current production data.

db/src/main/resources/sql/flyway/V102__add_indexes_to_domain_history_sub_tables.sql

@@ -0,0 +1,19 @@
+-- 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 INDEX IF NOT EXISTS domain_history_to_transaction_record_idx
+  ON "DomainTransactionRecord" (domain_repo_id, history_revision_id);
+
+CREATE INDEX IF NOT EXISTS domain_history_to_ds_data_history_idx
+  ON "DomainDsDataHistory" (domain_repo_id, domain_history_revision_id);