Don't create AvroData for each KafkaSourceRecord (apache#12859)

(cherry picked from commit 792a77e)

pulsar-io/kafka-connect-adaptor/src/main/java/org/apache/pulsar/io/kafka/connect/KafkaConnectSource.java

@@ -69,15 +69,12 @@ public synchronized KafkaSourceRecord processSourceRecord(final SourceRecord src
         return record;
     }
 
-    private static Map<String, String> PROPERTIES = Collections.emptyMap();
-    private static Optional<Long> RECORD_SEQUENCE = Optional.empty();
-    private static long FLUSH_TIMEOUT_MS = 2000;
+    private static final AvroData avroData = new AvroData(1000);
 
     private class KafkaSourceRecord extends AbstractKafkaSourceRecord<KeyValue<byte[], byte[]>> implements KVRecord<byte[], byte[]> {
 
         KafkaSourceRecord(SourceRecord srcRecord) {
             super(srcRecord);
-            AvroData avroData = new AvroData(1000);
             byte[] keyBytes = keyConverter.fromConnectData(
                     srcRecord.topic(), srcRecord.keySchema(), srcRecord.key());
             this.key = keyBytes != null ? Optional.of(Base64.getEncoder().encodeToString(keyBytes)) : Optional.empty();