SEC-2858: Add ANY_MESSAGE.toString()

messaging/src/main/java/org/springframework/security/messaging/util/matcher/MessageMatcher.java

@@ -39,5 +39,9 @@ public interface MessageMatcher<T> {
         public boolean matches(Message<? extends Object> message) {
             return true;
         }
+
+        public String toString() {
+            return "ANY_MESSAGE";
+        }
     };
 }