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/reference/scheduling/policies.md

@@ -0,0 +1,42 @@
+---
+title: 调度策略
+content_type: concept
+sitemap:
+  priority: 0.2 # Scheduling priorities are deprecated
+---
+
+<!--
+title: Scheduling Policies
+content_type: concept
+sitemap:
+  priority: 0.2 # Scheduling priorities are deprecated
+-->
+
+<!-- overview -->
+<!--
+In Kubernetes versions before v1.23, a scheduling policy can be used to specify the *predicates* and *priorities* process. For example, you can set a scheduling policy by
+running `kube-scheduler --policy-config-file <filename>` or `kube-scheduler --policy-configmap <ConfigMap>`.
+
+This scheduling policy is not supported since Kubernetes v1.23. Associated flags `policy-config-file`, `policy-configmap`, `policy-configmap-namespace` and `use-legacy-policy-config` are also not supported. Instead, use the [Scheduler Configuration](/docs/reference/scheduling/config/) to achieve similar behavior.
+-->
+
+在 Kubernetes v1.23 版本之前，可以使用调度策略来指定 *predicates* 和 *priorities* 进程。
+例如，可以通过运行 `kube-scheduler --policy-config-file <filename>` 或者
+ `kube-scheduler --policy-configmap <ConfigMap>` 设置调度策略。
+
+但是从 Kubernetes v1.23 版本开始，不再支持这种调度策略。
+同样地也不支持相关的 `policy-config-file`、 `policy-configmap`、 `policy-configmap-namespace` 以及 `use-legacy-policy-config` 标志。
+你可以通过使用 [调度配置](/zh/docs/reference/scheduling/config/)来实现类似的行为。
+
+## {{% heading "whatsnext" %}}
+
+<!--
+* Learn about [scheduling](/docs/concepts/scheduling-eviction/kube-scheduler/)
+* Learn about [kube-scheduler Configuration](/docs/reference/scheduling/config/)
+* Read the [kube-scheduler configuration reference (v1beta3)](/zh/docs/reference/config-api/kube-scheduler-config.v1beta3/)
+-->
+
+* 了解 [调度](/zh/docs/concepts/scheduling-eviction/kube-scheduler/)。
+* 了解 [kube-scheduler 配置](/zh/docs/reference/scheduling/config/)。
+* 阅读 [kube-scheduler 配置参考(v1beta3)](/zh/docs/reference/config-api/kube-scheduler-config.v1beta3/)。
+