(feat) add metrics on LcKafkaConsumer

Author: ylgrgyq

src/main/java/cn/leancloud/kafka/consumer/LcKafkaConsumer.java

@@ -1,9 +1,12 @@
 package cn.leancloud.kafka.consumer;
 
 import org.apache.kafka.clients.consumer.Consumer;
+import org.apache.kafka.common.Metric;
+import org.apache.kafka.common.MetricName;
 
 import java.io.Closeable;
 import java.util.Collection;
+import java.util.Map;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.TimeUnit;
 
@@ -80,6 +83,13 @@ public synchronized void subscribe(Collection<String> topics) {
         state = State.SUBSCRIBED;
     }
 
+    /**
+     * Get the metrics kept by the consumer
+     */
+    public Map<MetricName, ? extends Metric> metrics() {
+        return consumer.metrics();
+    }
+
     @Override
     public void close() {
         if (closed()) {