Refactor docs (#21627)

This patch:
- Rename some files( `.md` to `.en-us.md`), fix missed translation copy
- Update link which shoud be refer to `../hacking-on-gitea/` instead of
`../make/` (outdated)
- Update `_redirects`:
  -  redirect `/{zh-cn|fr-fr}/make/` to `../hacking-on-gitea/`
  - redirect `/zh-cn/third-party-tools/` to `/zh-cn/integrations/`
- Delete duplicated/outdated files.
- Update menu `weight` of developers.zh-cn.md

Signed-off-by: Xinyu Zhou <i@sourcehut.net>

docs/content/doc/developers.zh-cn.md

@@ -8,6 +8,6 @@ draft: false
 menu:
   sidebar:
     name: "开发者"
-    weight: 50
+    weight: 55
     identifier: "developers"
 ---