apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/api/AdminServiceAPI.java/ItemAPI/createItem
class ItemAPI:    public ItemDTO createItem(String appId, Env env, String clusterName, String namespace, ItemDTO item) {
      return restTemplate.post(env, "apps/{appId}/clusters/{clusterName}/namespaces/{namespaceName}/items",
          item, ItemDTO.class, appId, clusterName, namespace);
    }