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/examples/admin/resource/limit-range-pod-1.yaml

@@ -0,0 +1,37 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: busybox1
+spec:
+  containers:
+  - name: busybox-cnt01
+    image: busybox:1.28
+    command: ["/bin/sh"]
+    args: ["-c", "while true; do echo hello from cnt01; sleep 10;done"]
+    resources:
+      requests:
+        memory: "100Mi"
+        cpu: "100m"
+      limits:
+        memory: "200Mi"
+        cpu: "500m"
+  - name: busybox-cnt02
+    image: busybox:1.28
+    command: ["/bin/sh"]
+    args: ["-c", "while true; do echo hello from cnt02; sleep 10;done"]
+    resources:
+      requests:
+        memory: "100Mi"
+        cpu: "100m"
+  - name: busybox-cnt03
+    image: busybox:1.28
+    command: ["/bin/sh"]
+    args: ["-c", "while true; do echo hello from cnt03; sleep 10;done"]
+    resources:
+      limits:
+        memory: "200Mi"
+        cpu: "500m"
+  - name: busybox-cnt04
+    image: busybox:1.28
+    command: ["/bin/sh"]
+    args: ["-c", "while true; do echo hello from cnt04; sleep 10;done"]