User details page (#26713)

This PR implements a proposal to clean up the admin users table by
moving some information out to a separate user details page (which also
displays some additional information).

Other changes:
- move edit user page from `/admin/users/{id}` to
`/admin/users/{id}/edit` -> `/admin/users/{id}` now shows the user
details page
- show if user is instance administrator as a label instead of a
separate column
- separate explore users template into a page- and a shared one, to make
it possible to use it on the user details page
- fix issue where there was no margin between alert message and
following content on admin pages

<details>

<summary>Screenshots</summary>


![grafik](https://github.com/go-gitea/gitea/assets/47871822/1ad57ac9-f20a-45a4-8477-ffe572a41e9e)


![grafik](https://github.com/go-gitea/gitea/assets/47871822/25786ecd-cb9d-4c92-90f4-e7f4292c073b)


</details>

Partially resolves #25939

---------

Co-authored-by: Giteabot <teabot@gitea.io>

templates/admin/user/view.tmpl

@@ -0,0 +1,48 @@
+{{template "admin/layout_head" (dict "ctxData" . "pageClass" "admin view user")}}
+
+<div class="admin-setting-content">
+	<div class="admin-responsive-columns">
+		<div class="gt-f1">
+			<h4 class="ui top attached header">
+				{{.Title}}
+				<div class="ui right">
+					<a class="ui primary tiny button" href="{{.Link}}/edit">{{ctx.Locale.Tr "admin.users.edit"}}</a>
+				</div>
+			</h4>
+			<div class="ui attached segment">
+				{{template "admin/user/view_details" .}}
+			</div>
+		</div>
+		<div class="gt-f1">
+			<h4 class="ui top attached header">
+				{{ctx.Locale.Tr "admin.emails"}}
+				<div class="ui right">
+					{{.EmailsTotal}}
+				</div>
+			</h4>
+			<div class="ui attached segment">
+				{{template "admin/user/view_emails" .}}
+			</div>
+		</div>
+	</div>
+	<h4 class="ui top attached header">
+		{{ctx.Locale.Tr "admin.repositories"}}
+		<div class="ui right">
+			{{.ReposTotal}}
+		</div>
+	</h4>
+	<div class="ui attached segment">
+		{{template "explore/repo_list" .}}
+	</div>
+	<h4 class="ui top attached header">
+		{{ctx.Locale.Tr "settings.organization"}}
+		<div class="ui right">
+			{{.OrgsTotal}}
+		</div>
+	</h4>
+	<div class="ui attached segment">
+		{{template "explore/user_list" .}}
+	</div>
+</div>
+
+{{template "admin/layout_footer" .}}