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>

web_src/css/index.css

@@ -9,6 +9,7 @@
 
 @import "./shared/issuelist.css";
 @import "./shared/repoorg.css";
+@import "./shared/settings.css";
 
 @import "./features/dropzone.css";
 @import "./features/gitgraph.css";