Emit log message when parent circuit breaker trips (#47000) (#47073)

We emit a debug log message whenever a child circuit breaker trips (in
`ChildMemoryCircuitBreaker#circuitBreak(String, long)`) but we never
emit a log message when the parent circuit breaker trips. As this is
more likely to happen with the real memory circuit breaker it is not
possible to detect this in the logs. With this commit we add a log
message on the same log level (debug) when the parent circuit breaker
trips.

server/src/main/java/org/elasticsearch/indices/breaker/HierarchyCircuitBreakerService.java

@@ -339,6 +339,7 @@ public class HierarchyCircuitBreakerService extends CircuitBreakerService {
             // child circuit breakers is categorized as transient or permanent.
             CircuitBreaker.Durability durability = memoryUsed.transientChildUsage >= memoryUsed.permanentChildUsage ?
                 CircuitBreaker.Durability.TRANSIENT : CircuitBreaker.Durability.PERMANENT;
+            logger.debug("{}", message);
             throw new CircuitBreakingException(message.toString(), memoryUsed.totalUsage, parentLimit, durability);
         }
     }