Differentiate better between user settings and admin settings (#26538)

User settings page and admin settings page are too similar. I thinlk
this will be better of using `User Settings` and `Admin Settings` as the
navbar's title.

Before:

![image](https://github.com/go-gitea/gitea/assets/18380374/68db06f3-918b-41bc-b4d3-522b1057eb57)

![image](https://github.com/go-gitea/gitea/assets/18380374/24f53d91-54e1-410c-ad9b-438bb2c8069f)

After:

![image](https://github.com/go-gitea/gitea/assets/18380374/6600a872-d630-4ea6-a58f-d9ded7d38067)

![image](https://github.com/go-gitea/gitea/assets/18380374/501cde5d-9868-4cba-829d-ff8bafce695d)

templates/admin/navbar.tmpl

@@ -1,6 +1,6 @@
 <div class="flex-container-nav">
 	<div class="ui fluid vertical menu">
-		<div class="header item">{{.locale.Tr "settings"}}</div>
+		<div class="header item">{{.locale.Tr "admin.settings"}}</div>
 		<a class="{{if .PageIsAdminDashboard}}active {{end}}item" href="{{AppSubUrl}}/admin">
 			{{.locale.Tr "admin.dashboard"}}
 		</a>