Add details summary for vertical menus in settings to allow toggling (#25098)

Close #25051
[referenced
answer](https://stackoverflow.com/questions/10813581/can-i-replace-the-expand-icon-of-the-details-element/69722686#69722686)
for marker overwrite. One limitation is that fomantic does not have
hover and active effects for the vertical submenu
([reference](https://fomantic-ui.com/collections/menu.html#sub-menu)).
And we might need to overwrite some styles if hover and active effects
are needed.

Update:
Used `data:image/svg` instead of `marker` content. And adjusted styles
for hover effect.

Take admin settings as an example:

https://github.com/go-gitea/gitea/assets/17645053/63f69823-ef43-47d5-a518-544b5ea35ba6

---------

Co-authored-by: silverwind <me@silverwind.io>

templates/user/settings/navbar.tmpl

@@ -20,8 +20,8 @@
 			{{.locale.Tr "settings.ssh_gpg_keys"}}
 		</a>
 		{{if .EnableActions}}
-		<div class="item">
-			{{.locale.Tr "actions.actions"}}
+		<details class="item toggleable-item" {{if or .PageIsSharedSettingsRunners .PageIsSharedSettingsSecrets}}open{{end}}>
+			<summary>{{.locale.Tr "actions.actions"}}</summary>
 			<div class="menu">
 				<a class="{{if .PageIsSharedSettingsRunners}}active {{end}}item" href="{{AppSubUrl}}/user/settings/actions/runners">
 					{{.locale.Tr "actions.runners"}}
@@ -30,7 +30,7 @@
 					{{.locale.Tr "secrets.secrets"}}
 				</a>
 			</div>
-		</div>
+		</details>
 		{{end}}
 		{{if .EnablePackages}}
 		<a class="{{if .PageIsSettingsPackages}}active {{end}}item" href="{{AppSubUrl}}/user/settings/packages">