[FLINK-36876] Optimize io thread number

Author: chenyuzhi

flink-kubernetes-operator/src/main/java/org/apache/flink/kubernetes/operator/config/KubernetesOperatorConfigOptions.java

@@ -119,7 +119,7 @@ public static String operatorConfigKey(String key) {
     public static final ConfigOption<Integer> OPERATOR_FLINK_CLIENT_IO_THREADS =
             operatorConfig("flink.client.io.threads")
                     .intType()
-                    .defaultValue(60)
+                    .defaultValue(10)
                     .withDescription(
                             "The maximum number of io threads used by the flink rest client.");