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_emails.tmpl

@@ -0,0 +1,19 @@
+<div class="flex-list">
+	{{range .Emails}}
+		<div class="flex-item">
+			<div class="flex-item-main">
+				<div class="flex-text-block">
+					{{.Email}}
+					{{if .IsPrimary}}
+						<div class="ui primary label">{{ctx.Locale.Tr "settings.primary"}}</div>
+					{{end}}
+					{{if .IsActivated}}
+						<div class="ui green label">{{ctx.Locale.Tr "settings.activated"}}</div>
+					{{else}}
+						<div class="ui label">{{ctx.Locale.Tr "settings.requires_activation"}}</div>
+					{{end}}
+				</div>
+			</div>
+		</div>
+	{{end}}
+</div>