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/packages/composer.en-us.md

@@ -1,7 +1,7 @@
 ---
 date: "2021-07-20T00:00:00+00:00"
 title: "Composer Packages Repository"
-slug: "packages/composer"
+slug: "usage/packages/composer"
 draft: false
 toc: false
 menu:
@@ -60,7 +60,7 @@ curl --user your_username:your_password_or_token \
      https://gitea.example.com/api/packages/testuser/composer?version=1.0.3
 ```
 
-If you are using 2FA or OAuth use a [personal access token]({{< relref "doc/developers/api-usage.en-us.md#authentication" >}}) instead of the password.
+If you are using 2FA or OAuth use a [personal access token]({{< relref "doc/development/api-usage.en-us.md#authentication" >}}) instead of the password.
 
 The server responds with the following HTTP Status codes.