Fix ReadEntryProcessor v2 SchedulingDelayStats (apache#3758)

Descriptions of the changes in this PR:



### Motivation

We registered `ReadEntrySchedulingDelayStats` of `ReadEntryProcessor` as `WriteThreadQueuedLatency` mistakenly, so we need fix it.

### Changes

Register `ReadEntrySchedulingDelayStats`  if `ReadEntryProcessor`

Author: AnonHxy

bookkeeper-server/src/main/java/org/apache/bookkeeper/proto/PacketProcessorBase.java

@@ -166,8 +166,15 @@ protected void sendResponseAndWait(int rc, Object response, OpStatsLogger statsL
 
     @Override
     public void run() {
-        requestProcessor.getRequestStats().getWriteThreadQueuedLatency()
-                .registerSuccessfulEvent(MathUtils.elapsedNanos(enqueueNanos), TimeUnit.NANOSECONDS);
+        if (request instanceof BookieProtocol.ReadRequest) {
+            requestProcessor.getRequestStats().getReadEntrySchedulingDelayStats()
+                    .registerSuccessfulEvent(MathUtils.elapsedNanos(enqueueNanos), TimeUnit.NANOSECONDS);
+        }
+        if (request instanceof BookieProtocol.ParsedAddRequest) {
+            requestProcessor.getRequestStats().getWriteThreadQueuedLatency()
+                    .registerSuccessfulEvent(MathUtils.elapsedNanos(enqueueNanos), TimeUnit.NANOSECONDS);
+        }
+
         if (!isVersionCompatible()) {
             sendResponse(BookieProtocol.EBADVERSION,
                          ResponseBuilder.buildErrorResponse(BookieProtocol.EBADVERSION, request),