[FLINK-37304][connector/kafka] Downgrade the log level of metadataUpdateEvent in DynamicKafkaSourceEnumerator to avoid displaying connection information

This closes #153.

Author: lvyanquan

flink-connector-kafka/src/main/java/org/apache/flink/connector/kafka/dynamic/source/enumerator/DynamicKafkaSourceEnumerator.java

@@ -347,7 +347,7 @@ private Set<KafkaStream> handleFetchSubscribedStreamsError(
     private void sendMetadataUpdateEventToAvailableReaders() {
         for (int readerId : enumContext.registeredReaders().keySet()) {
             MetadataUpdateEvent metadataUpdateEvent = new MetadataUpdateEvent(latestKafkaStreams);
-            logger.info("sending metadata update to reader {}: {}", readerId, metadataUpdateEvent);
+            logger.debug("sending metadata update to reader {}: {}", readerId, metadataUpdateEvent);
             enumContext.sendEventToSourceReader(readerId, metadataUpdateEvent);
         }
     }
@@ -517,7 +517,8 @@ public void handleSourceEvent(int subtaskId, SourceEvent sourceEvent) {
 
         if (enumContext.registeredReaders().containsKey(subtaskId)) {
             MetadataUpdateEvent metadataUpdateEvent = new MetadataUpdateEvent(latestKafkaStreams);
-            logger.info("sending metadata update to reader {}: {}", subtaskId, metadataUpdateEvent);
+            logger.debug(
+                    "sending metadata update to reader {}: {}", subtaskId, metadataUpdateEvent);
             enumContext.sendEventToSourceReader(subtaskId, metadataUpdateEvent);
         } else {
             logger.warn("Got get metadata update but subtask was unavailable");