Add a SQL schema and DAO for KmsSecretRevision (#840)

* Add a SQL schema and DAO for KmsSecretRevision

The dual-object nature of KmsSecret and KmsSecretRevision will not be
necessary once we have moved to SQL. In that world, the only object will
be the one now called KmsSecretRevision. KmsSecretRevision already
stores its parent so all we need to do is convert that key to the String
secretName (or from the secretName to the key, if loading from SQL) and
select the max revision ID for a given secret name.

In a future PR, we will add a dual-writing DAO to these objects and
perform the dual writes, similar to how ReservedList functions.

* Regenerate diagram

* Rename revisionId and cryptoKeyVersionName

* Fix SQL files and diagram

db/src/main/resources/sql/flyway/V71__create_kms_secret.sql

@@ -0,0 +1,24 @@
+-- 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.
+
+CREATE TABLE "KmsSecret" (
+   revision_id  int8 NOT NULL,
+    creation_time timestamptz NOT NULL,
+    encrypted_value text NOT NULL,
+    crypto_key_version_name text NOT NULL,
+    secret_name text NOT NULL,
+    PRIMARY KEY (revision_id)
+);
+
+CREATE INDEX IDXli9nil3s4t4p21i3xluvvilb7 ON "KmsSecret" (secret_name);