Remove unnecessary Boolean boxing (#1667)

### Motivation

There is some unnecessary boxing of `boolean` primitives in the code.
This PR removes that boxing.

### Modifications

* Replace `Boolean` with `boolean` when appropriate.

### Verifying this change

No new tests are added, but the changes are pretty minor and are easy to
understand. In all cases, we can see that the calling methods and the
usage of the variables expect a primitive `boolean`.

(cherry picked from commit bc1dee1)

kafka-impl/src/main/java/io/streamnative/pulsar/handlers/kop/KafkaCommandDecoder.java

@@ -177,7 +177,7 @@ protected static ByteBuf responseToByteBuf(AbstractResponse response, KafkaHeade
         }
     }
 
-    protected Boolean channelReady() {
+    protected boolean channelReady() {
         return hasAuthenticated();
     }
 

kafka-impl/src/main/java/io/streamnative/pulsar/handlers/kop/coordinator/transaction/TransactionCoordinator.java

@@ -555,7 +555,7 @@ private void endTransaction(String transactionalId,
                                 Long producerId,
                                 Short producerEpoch,
                                 TransactionResult txnMarkerResult,
-                                Boolean isFromClient,
+                                boolean isFromClient,
                                 Consumer<Errors> callback) {
         AtomicBoolean isEpochFence = new AtomicBoolean(false);
         if (transactionalId == null || transactionalId.isEmpty()) {

kafka-impl/src/main/java/io/streamnative/pulsar/handlers/kop/coordinator/transaction/TransactionMetadata.java

@@ -387,7 +387,7 @@ private static class BumpEpochResult {
     public TxnTransitMetadata prepareProducerIdRotation(Long newProducerId,
                                   Integer newTxnTimeoutMs,
                                   Long updateTimestamp,
-                                  Boolean recordLastEpoch) {
+                                  boolean recordLastEpoch) {
         if (hasPendingTransaction()) {
             throw new IllegalStateException("Cannot rotate producer ids while a transaction is still pending");
         }
@@ -489,7 +489,7 @@ public void addPartitions(Set<TopicPartition> partitions) {
         topicPartitions.addAll(partitions);
     }
 
-    public Boolean pendingTransitionInProgress() {
+    public boolean pendingTransitionInProgress() {
         return this.pendingState.isPresent();
     }
 

kafka-impl/src/main/java/io/streamnative/pulsar/handlers/kop/stats/PrometheusTextFormatUtil.java

@@ -90,9 +90,9 @@ public static void writeOpStat(SimpleTextOutputStream w, String name, DataSketch
     }
 
     private static void writeQuantile(SimpleTextOutputStream w, DataSketchesOpStatsLogger opStat, String name,
-                                      Boolean success, double quantile) {
+                                      boolean success, double quantile) {
         w.write(name)
-                .write("{success=\"").write(success.toString())
+                .write("{success=\"").write(success)
                 .write("\",quantile=\"").write(Double.toString(quantile));
         if (!opStat.getLabels().isEmpty()) {
             w.write("\", ");
@@ -105,8 +105,8 @@ private static void writeQuantile(SimpleTextOutputStream w, DataSketchesOpStatsL
     }
 
     private static void writeCount(SimpleTextOutputStream w, DataSketchesOpStatsLogger opStat, String name,
-                                   Boolean success) {
-        w.write(name).write("_count{success=\"").write(success.toString());
+                                   boolean success) {
+        w.write(name).write("_count{success=\"").write(success);
         if (!opStat.getLabels().isEmpty()) {
             w.write("\", ");
             writeLabelsNoBraces(w, opStat.getLabels());
@@ -118,8 +118,8 @@ private static void writeCount(SimpleTextOutputStream w, DataSketchesOpStatsLogg
     }
 
     private static void writeSum(SimpleTextOutputStream w, DataSketchesOpStatsLogger opStat, String name,
-                                 Boolean success) {
-        w.write(name).write("_sum{success=\"").write(success.toString());
+                                 boolean success) {
+        w.write(name).write("_sum{success=\"").write(success);
         if (!opStat.getLabels().isEmpty()) {
             w.write("\", ");
             writeLabelsNoBraces(w, opStat.getLabels());