Increase the number of buckets in the queue latency histogram (#137596)

Author: nicktindall

server/src/main/java/org/elasticsearch/common/util/concurrent/TaskExecutionTimeTrackingEsThreadPoolExecutor.java

@@ -39,7 +39,8 @@
  * An extension to thread pool executor, which tracks statistics for the task execution time.
  */
 public final class TaskExecutionTimeTrackingEsThreadPoolExecutor extends EsThreadPoolExecutor {
-    public static final int QUEUE_LATENCY_HISTOGRAM_BUCKETS = 18;
+    // 20 buckets means the upper bound on the largest bound bucket will be 2^18 ms (~= 4 minutes 20 seconds)
+    public static final int QUEUE_LATENCY_HISTOGRAM_BUCKETS = 20;
     private static final int[] LATENCY_PERCENTILES_TO_REPORT = { 50, 90, 99 };
 
     private final Function<Runnable, WrappedRunnable> runnableWrapper;