[client] Change the default value of 'netty.client.num-network-threads' to 3 to avoid netty channel congestion (apache#1642)

Author: swuferhong

fluss-common/src/main/java/org/apache/fluss/config/ConfigOptions.java

@@ -739,10 +739,10 @@ public class ConfigOptions {
     public static final ConfigOption<Integer> NETTY_CLIENT_NUM_NETWORK_THREADS =
             key("netty.client.num-network-threads")
                     .intType()
-                    .defaultValue(1)
+                    .defaultValue(3)
                     .withDescription(
                             "The number of threads that the client uses for sending requests to the "
-                                    + "network and receiving responses from network. The default value is 1");
+                                    + "network and receiving responses from network. The default value is 3");
 
     // ------------------------------------------------------------------------
     //  Client Settings

website/docs/maintenance/configuration.md

@@ -89,7 +89,7 @@ during the Fluss cluster working.
 | netty.server.num-worker-threads  | Integer  | 8       | The number of threads that the server uses for processing requests, which may include disk and remote I/O.                                  |
 | netty.server.max-queued-requests | Integer  | 500     | The number of queued requests allowed for worker threads, before blocking the I/O threads.                                                  |
 | netty.connection.max-idle-time   | Duration | 10min   | Close idle connections after the given time specified by this config.                                                                       |
-| netty.client.num-network-threads | Integer  | 1       | The number of threads that the client uses for sending requests to the network and receiving responses from network. The default value is 1 |
+| netty.client.num-network-threads | Integer  | 3       | The number of threads that the client uses for sending requests to the network and receiving responses from network. The default value is 3 |
 
 ## Log