CKS: make clustertype optional to keep backwards compatibility (#8180)

This PR fixes the issue that 4.18 cmk/api to create CKS cluster does not work in 4.19

Author: weizhouapache

plugins/integrations/kubernetes-service/src/main/java/org/apache/cloudstack/api/command/user/kubernetes/cluster/CreateKubernetesClusterCmd.java

@@ -145,7 +145,7 @@ public class CreateKubernetesClusterCmd extends BaseAsyncCreateCmd {
             description = "root disk size in GB for each node")
     private Long nodeRootDiskSize;
 
-    @Parameter(name = ApiConstants.CLUSTER_TYPE, type = CommandType.STRING, required = true, description = "type of the cluster: CloudManaged, ExternalManaged", since="4.19.0")
+    @Parameter(name = ApiConstants.CLUSTER_TYPE, type = CommandType.STRING, description = "type of the cluster: CloudManaged, ExternalManaged. The default value is CloudManaged.", since="4.19.0")
     private String clusterType;
 
     /////////////////////////////////////////////////////