INT-4196: MongoOutGateway: add CollectionCallback

JIRA: https://jira.spring.io/browse/INT-4196

Add `CollectionCallback` option to the `MongoDbOutboundGateway`

Add XML support to CollectionCallback

Fix PR comments

Fix issue with javadoc parsing

* Polishing code style, JavaDocs and some Docs

spring-integration-core/src/test/java/org/springframework/integration/configuration/EnableIntegrationTests.java

@@ -950,7 +950,7 @@ public class EnableIntegrationTests {
 		@Bean
 		@ServiceActivator(inputChannel = "controlBusChannel")
 		@Role("bar")
-		public ExpressionControlBusFactoryBean controlBus() throws Exception {
+		public ExpressionControlBusFactoryBean controlBus() {
 			return new ExpressionControlBusFactoryBean();
 		}