[Improvement-14658][etcd] Distinguish between add and update by using pre kv (#14659)

Co-authored-by: eye <eye.gu@aloudata.com>

dolphinscheduler-registry/dolphinscheduler-registry-plugins/dolphinscheduler-registry-etcd/src/main/java/org/apache/dolphinscheduler/plugin/registry/etcd/EtcdRegistry.java

@@ -151,7 +151,8 @@ public class EtcdRegistry implements Registry {
     public boolean subscribe(String path, SubscribeListener listener) {
         try {
             ByteSequence watchKey = byteSequence(path);
-            WatchOption watchOption = WatchOption.newBuilder().isPrefix(true).build();
+            WatchOption watchOption =
+                    WatchOption.newBuilder().withPrevKV(true).isPrefix(true).build();
             watcherMap.computeIfAbsent(path,
                     $ -> client.getWatchClient().watch(watchKey, watchOption, watchResponse -> {
                         for (WatchEvent event : watchResponse.getEvents()) {
@@ -352,7 +353,11 @@ public class EtcdRegistry implements Registry {
 
             switch (event.getEventType()) {
                 case PUT:
+                    if (event.getPrevKV().getKey().isEmpty()) {
                         type(Type.ADD);
+                    } else {
+                        type(Type.UPDATE);
+                    }
                     break;
                 case DELETE:
                     type(Type.REMOVE);