Add docs for Spring Integration DynamoDB support (#1472)

Author: artembilan

docs/src/main/asciidoc/dynamodb.adoc

@@ -186,3 +186,31 @@ Note that `DynamoDbClientCustomizer` beans are applied **after** `AwsSyncClientC
 
 Since it depends on how you will use DynamoDb integration providing a list of IAM policies would be pointless since least privilege model should be used.
 To check what IAM policies DynamoDb uses and see which ones you should use please check https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/using-identity-based-policies.html[IAM policies]
+
+=== Spring Integration Support
+
+Starting with version 4.0, Spring Cloud AWS provides https://spring.io/projects/spring-integration[Spring Integration] components for Amazon DynamoDB.
+
+The `DynamoDbMetadataStore` is a https://docs.spring.io/spring-integration/reference/meta-data-store.html[`ConcurrentMetadataStore`] implementation to store and retrieve key-value entries in the specific DynamoDB.
+It requires a `DynamoDbAsyncClient` and default table name is `SpringIntegrationMetadataStore`.
+If the table is not present, the `DynamoDbMetadataStore` creates it on its initialization issuing an async `dynamoDB.createTable()` request.
+The table structure is like:
+
+- the `metadataKey` is a string table key as a hash;
+- the `metadataValue` is a string for entry value;
+- the `expireAt` is time-to-live attribute according to respective algorithm in DynamoDB.
+
+See `DynamoDbMetadataStore` Javadocs for more information.
+
+The `DynamoDbLockRegistry` is an `ExpirableLockRegistry` and `RenewableLockRegistry` implementation for the https://docs.spring.io/spring-integration/reference/distributed-locks.html[`DistributedLock`] abstraction based on DynamoDB table.
+The supporting `DynamoDbLockRepository` class is for DynamoDB table management and low-level DynamoDB API interaction.
+It requires a `DynamoDbAsyncClient`, and the default table name is `SpringIntegrationLockRegistry`.
+
+The table structure is like:
+
+- the `lockKey` is a string table key as a hash;
+- the `lockOwner` is a string for lock record ownership — the instance which holds the lock at the moment;
+- the `createdAt` is an `Instant.now().getEpochSecond()` when the lock record was created;
+- the `expireAt` is time-to-live attribute according to respective algorithm in DynamoDB.
+
+See `DynamoDbLockRegistry` and `DynamoDbLockRepository` Javadocs for more information.