INT-4081: Custom PreparedStSetter for JdbcMChStore

JIRA: https://jira.spring.io/browse/INT-4081

* Add `MessageGroupPreparedStatementSetter` to let end-user to override
the message insertion logic
* Add tests and Docs

src/reference/asciidoc/jdbc.adoc

@@ -365,6 +365,37 @@ If your database is not listed, you can easily extend the `AbstractChannelMessag
 
 Since _version 4.0_, the `MESSAGE_SEQUENCE` column has been added to the table to ensure first-in-first-out (FIFO) queueing even when messages are stored in the same millisecond.
 
+Since_version 5.0, by overloading `MessageGroupPreparedStatementSetter` class you can provide custom 
+implementation to `PreparedStatementSetter` to support different columns or table structure 
+or serialization strategy.
+For example, instead of default serialization to byte[], we can store its structure in JSON string.
+
+Below example uses the default implementation of `setValues` to store common columns and overrides the behavior 
+just to store the message payload as varchar.
+
+[source,java]
+----
+
+public class CustomMessageGroupPreparedStatementSetter 
+		extends MessageGroupPreparedStatementSetter {
+
+	public CustomMessageGroupPreparedStatementSetter() {
+		super();
+	}
+
+	@Override
+	public void setValues(PreparedStatement preparedStatement, Message<?> requestMessage, 
+		Object groupId, String region, 	boolean priorityEnabled) throws SQLException {
+		// Populate common columns
+		super.setValues(preparedStatement, requestMessage, groupId, region, priorityEnabled);
+		// Store message payload as varchar
+		preparedStatement.setString(6, requestMessage.getPayload().toString());
+	}	
+}
+
+
+----
+
 [IMPORTANT]
 =====
 Generally it is not recommended to use a relational database for the purpose of queuing.

src/reference/asciidoc/whats-new.adoc

@@ -291,3 +291,10 @@ See <<ip>> for more information.
 The `GemfireMetadataStore` now implements `ListenableMetadataStore`, allowing users to listen to cache events by providing `MetadataStoreListener` instances to the store.
 
 See <<gemfire>> for more information.
+
+==== Jdbc Message Channel Store Changes
+
+The `JdbcMessageChannelStore` now provides setter to set `MessageGroupPreparedStatementSetter`, 
+allowing users to easily customize `PreparedStatementSetter` in the store.
+
+See <<jdbc-message-store-channels>> for more information.