Switch language name 'zh' to 'zh-cn'

This is the first step to rename 'zh' to 'zh-cn'. There are several reasons why we rename the language name.

- The upstream docsy theme changed the language name, leading to many warnings during site build;
  The side-effect is that the i18n strings are no longer working.
- We believe renaming the language is the right thing to do, because this move can make room for other variants of Chinese language, such as 'zh-tw', 'zh-sg' etc.

There would be several follow-ups to this PR, such as fixing the intra-site links, adding redirects etc.

We will lock up changes to zh/zh-cn pages for the moment, until this one gets in.

This PR is based on commit cdad0a7342.

content/zh-cn/docs/tasks/administer-cluster/network-policy-provider/antrea-network-policy.md

@@ -0,0 +1,49 @@
+---
+title: 使用 Antrea 提供 NetworkPolicy
+content_type: task
+weight: 10
+---
+<!--
+---
+title: Use Antrea for NetworkPolicy
+content_type: task
+weight: 10
+---
+-->
+
+<!-- overview -->
+<!--
+This page shows how to install and use Antrea CNI plugin on Kubernetes.
+For background on Project Antrea, read the [Introduction to Antrea](https://antrea.io/docs/).
+-->
+本页展示了如何在 kubernetes 中安装和使用 Antrea CNI 插件。
+要了解 Antrea 项目的背景，请阅读 [Antrea 介绍](https://antrea.io/docs/)。
+
+## {{% heading "prerequisites" %}}
+
+<!--
+You need to have a Kubernetes cluster. Follow the
+[kubeadm getting started guide](/docs/reference/setup-tools/kubeadm/) to bootstrap one.
+-->
+你需要拥有一个 kuernetes 集群。
+遵循 [kubeadm 入门指南](/zh/docs/reference/setup-tools/kubeadm/)自行创建一个。
+
+<!-- steps -->
+
+<!--
+## Deploying Antrea with kubeadm
+
+Follow [Getting Started](https://github.com/vmware-tanzu/antrea/blob/main/docs/getting-started.md) guide to deploy Antrea for kubeadm.
+-->
+## 使用 kubeadm 部署 Antrea
+遵循[入门](https://github.com/vmware-tanzu/antrea/blob/main/docs/getting-started.md)指南
+为 kubeadm 部署 Antrea 。
+
+## {{% heading "whatsnext" %}}
+
+<!--
+Once your cluster is running, you can follow the [Declare Network Policy](/docs/tasks/administer-cluster/declare-network-policy/) to try out Kubernetes NetworkPolicy.
+-->
+一旦你的集群已经运行，你可以遵循 
+[声明网络策略](/zh/docs/tasks/administer-cluster/declare-network-policy/)
+来尝试 Kubernetes NetworkPolicy。