[docs] add zh docs (#3507)

* [docs] add zh docs

* [docs] add lang dropdown

* [docs] update mkdocs zh config

* [docs] migrate assets

* [docs] update overrides dir in mkdocs zh config

* [docs] exclude locales director in main mkdocs config

* [docs] rename assets to public to avoid conflicting with template

* [docs] extra_css change followup

* [docs] add theme.palette.toggle.icon back into mkdocs zh config

* [docs] fix zh readme reference + migrate language-specific repo markdown to docs

* [docs] translate remaining repo docs + update reference

* [docs] update zh index.md reference

* [docs/zh] wording alignment

docs/locales/zh/index.md

@@ -0,0 +1,17 @@
+{%
+  include "./repo/README.md"
+  start='<!--overview-start-->'
+  end='<!--overview-end-->'
+%}
+
+{%
+  include "./repo/README.md"
+  start='<!--body-1-start-->'
+  end='<!--body-1-end-->'
+%}
+
+{%
+  include "./repo/README.md"
+  start='<!--body-2-start-->'
+  end='<!--body-2-end-->'
+%}