Restructure documentation. Now the documentation has installation, administration, usage, development, contributing the 5 main parts (#23629)

- **Installation**: includes how to install Gitea and related other
tools, also includes upgrade Gitea
- **Administration**: includes how to configure Gitea, customize Gitea
and manage Gitea instance out of Gitea admin UI
- **Usage**: includes how to use Gitea's functionalities. A sub
documentation is about packages, in future we could also include CI/CD
and others.
- **Development**: includes how to integrate with Gitea's API, how to
develop new features within Gitea
- **Contributing**: includes how to contribute code to Gitea
repositories.

After this is merged, I think we can have a sub-documentation of `Usage`
part named `Actions` to describe how to use Gitea actions

---------

Co-authored-by: John Olheiser <john.olheiser@gmail.com>

docs/content/doc/usage/linked-references.en-us.md

@@ -96,7 +96,7 @@ Sometimes a commit or pull request may fix or bring back a problem documented
 in a particular issue. Gitea supports closing and reopening the referenced
 issues by preceding the reference with a particular _keyword_. Common keywords
 include "closes", "fixes", "reopens", etc. This list can be
-[customized]({{< ref "/doc/advanced/config-cheat-sheet.en-us.md" >}}) by the
+[customized]({{< ref "doc/administration/config-cheat-sheet.en-us.md" >}}) by the
 site administrator.
 
 Example: