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/enable-disable-api.md

@@ -0,0 +1,61 @@
+---
+title: 启用/禁用 Kubernetes API
+content_type: task
+---
+<!-- 
+---
+title: Enable Or Disable A Kubernetes API
+content_type: task
+---
+-->
+
+<!-- overview -->
+<!-- 
+This page shows how to enable or disable an API version from your cluster's
+{{< glossary_tooltip text="control plane" term_id="control-plane" >}}.
+-->
+本页展示怎么用集群的
+{{< glossary_tooltip text="控制平面" term_id="control-plane" >}}.
+启用/禁用 API 版本。
+
+<!-- steps -->
+
+
+<!-- 
+Specific API versions can be turned on or off by passing `--runtime-config=api/<version>` as a
+command line argument to the API server. The values for this argument are a comma-separated
+list of API versions. Later values override earlier values.
+
+The `runtime-config` command line argument also supports 2 special keys:
+-->
+通过 API 服务器的命令行参数 `--runtime-config=api/<version>` ，
+可以开启/关闭某个指定的 API 版本。
+此参数的值是一个逗号分隔的 API 版本列表。
+此列表中，后面的值可以覆盖前面的值。
+
+命令行参数 `runtime-config` 支持两个特殊的值（keys）：
+
+<!-- 
+- `api/all`, representing all known APIs
+- `api/legacy`, representing only legacy APIs. Legacy APIs are any APIs that have been
+   explicitly [deprecated](/zh/docs/reference/using-api/deprecation-policy/).
+
+For example, to turning off all API versions except v1, pass `--runtime-config=api/all=false,api/v1=true`
+to the `kube-apiserver`.
+-->
+- `api/all`：指所有已知的 API
+- `api/legacy`：指过时的 API。过时的 API 就是明确地
+  [弃用](/zh/docs/reference/using-api/deprecation-policy/)
+  的 API。
+
+例如：为了停用除去 v1 版本之外的全部其他 API 版本，
+就用参数 `--runtime-config=api/all=false,api/v1=true` 启动 `kube-apiserver`。
+
+## {{% heading "whatsnext" %}}
+
+<!-- 
+Read the [full documentation](/docs/reference/command-line-tools-reference/kube-apiserver/)
+for the `kube-apiserver` component.
+-->
+阅读[完整的文档](/zh/docs/reference/command-line-tools-reference/kube-apiserver/),
+以了解 `kube-apiserver` 组件。