INT-4477: Add getRole() to LeaderInitiator Context

JIRA: https://jira.spring.io/browse/INT-4477

When running multiple roles, it is useful to be able to determine the
role for a particular context, e.g. in an event.

* Docs

**cherry-pick to 5.0.x**

(cherry picked from commit 73dbdb8)

src/reference/asciidoc/endpoint.adoc

@@ -704,8 +704,24 @@ An example of this is a file inbound channel adapter that is polling a shared di
 To participate in a leader election and be notified when elected leader, when leadership is revoked or, failure to acquire the resources to become leader, an application creates a component in the application context called a "leader initiator".
 Normally a leader initiator is a `SmartLifecycle` so it starts up (optionally) automatically when the context starts, and then publishes notifications when leadership changes.
 Users can also receive failure notifications by setting the `publishFailedEvents` to `true` (starting with _version 5.0_), in cases when they want take a specific action if a failure occurs.
-By convention the user provides a `Candidate` that receives the callbacks and also can revoke the leadership through a `Context` object provided by the framework.
-User code can also listen for `org.springframework.integration.leader.event.AbstractLeaderEvent` s, and respond accordingly, for instance using a `SmartLifecycleRoleController`.
+By convention, the user provides a `Candidate` that receives the callbacks and also can revoke the leadership through a `Context` object provided by the framework.
+User code can also listen for `org.springframework.integration.leader.event.AbstractLeaderEvent` s (the super class of `OnGrantedEvent` and `OnRevokedEvent`), and respond accordingly, for instance using a `SmartLifecycleRoleController`.
+The events contain a reference to the `Context` object:
+
+[source, java]
+----
+public interface Context {
+
+	boolean isLeader();
+
+	void yield();
+
+	String getRole();
+
+}
+----
+
+Starting with _version 5.0.6_, the context provides a reference to the candidate's role.
 
 There is a basic implementation of a leader initiator based on the `LockRegistry` abstraction.
 To use it you just need to create an instance as a bean, for example: