INT-3950: Fix Aggregator documentation

JIRA: https://jira.spring.io/browse/INT-3950

Previously there was a mention of the `MessageGroupStore.expireMessageGroup(groupId)` which just doesn't existing
in the Framework and never has been there.

* Fix the documentation for the existing `MessageGroupStore.expireMessageGroups(timeout)`.
Although the mention there of `Control Bus` requires to have `@ManagedOperation` on the method.

* Add `@ManagedOperation` for the `MessageGroupStore.expireMessageGroups(timeout)` and confirm with the test-case: `AggregatorWithMessageStoreParserTests`
* Fix the same docs in the XSD for `<aggregator>`
* Fix other typos in the `aggregator.adoc` and `resequencer.adoc`

spring-integration-mongodb/src/main/java/org/springframework/integration/mongodb/store/ConfigurableMongoDbMessageStore.java

@@ -36,6 +36,7 @@ import org.springframework.integration.store.MessageGroupMetadata;
 import org.springframework.integration.store.MessageGroupStore;
 import org.springframework.integration.store.MessageStore;
 import org.springframework.jmx.export.annotation.ManagedAttribute;
+import org.springframework.jmx.export.annotation.ManagedOperation;
 import org.springframework.messaging.Message;
 import org.springframework.util.Assert;
 
@@ -289,6 +290,7 @@ public class ConfigurableMongoDbMessageStore extends AbstractConfigurableMongoDb
 	}
 
 	@Override
+	@ManagedOperation
 	public int expireMessageGroups(long timeout) {
 		int count = 0;
 		long threshold = System.currentTimeMillis() - timeout;