Build Dynamo DB backed Message Store (#358)

* Work in progress...

* Finish first pass draft of MessagesDynamoDb

* Use begins_with everywhere for destination device id

* Remove now unused methods

* First basic test built

* Add another test case

* Remove comment

* Verify more of the message contents

* Ensure all methods are tested

* Integrate MessagesDynamoDb into the MessagesManager

This change plugs the MessagesDynamoDb class into the live serving
flow in MessagesManager.

Tests are not yet as comprehensive for this big a change as they
should be, but they now compile and pass so checkpointing here with a
commit.

* Put DynamoDB before RDBS when deleting specific messages

* Extract method

* Make aws sdk version into a property

* Rename clientBuilder

* Discard messages with no GUID

* Unify batching logic into one function

* Comment on the source of the value in this constant

* Inline method

* Variable name swizzle

* Add timers to all public methods

* Add missing return statements

* Reject messages that are too large with response code 413

* Add configuration to control dynamo DB timeouts

* Set server timestamp from the ReceiptSender

* Change to shorter key names to optimize IOPS

* Fix tests broken by changing column names

* Fix broken copyright template output

* Remove copyright template error text

* Add experiments to control use of dynamo and rds in message storage

* Specify instance profile credentials for the dynamic configuration manager

* Use property for aws sdk version

* Switch dynamo to instance profile credentials

* Add metrics to the batch write loop

* Use placeholders in logging

service/src/main/java/org/whispersystems/textsecuregcm/configuration/MessageDynamoDbConfiguration.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2021 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.configuration;
+
+import javax.validation.Valid;
+import javax.validation.constraints.NotEmpty;
+import java.time.Duration;
+
+public class MessageDynamoDbConfiguration {
+  private String region;
+  private String tableName;
+  private Duration timeToLive = Duration.ofDays(7);
+  private Duration clientExecutionTimeout = Duration.ofSeconds(30);
+  private Duration clientRequestTimeout = Duration.ofSeconds(10);
+
+  @Valid
+  @NotEmpty
+  public String getRegion() {
+    return region;
+  }
+
+  @Valid
+  @NotEmpty
+  public String getTableName() {
+    return tableName;
+  }
+
+  @Valid
+  public Duration getTimeToLive() {
+    return timeToLive;
+  }
+
+  public Duration getClientExecutionTimeout() {
+    return clientExecutionTimeout;
+  }
+
+  public Duration getClientRequestTimeout() {
+    return clientRequestTimeout;
+  }
+}