Display deprecated warning in admin panel pages as well as in the log file (#26094)

This PR includes #26007 's changes but have a UI to prompt administrator
about the deprecated settings as well as the log or console warning.
Then users will have enough time to notice the problem and don't have
surprise like before.

<img width="1293" alt="图片"
src="https://github.com/go-gitea/gitea/assets/81045/c33355f0-1ea7-4fb3-ad43-cd23cd15391d">

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/admin/layout_head.tmpl

@@ -1,9 +1,11 @@
 {{template "base/head" .ctxData}}
 <div role="main" aria-label="{{.ctxData.Title}}" class="page-content {{.pageClass}}">
+	<div class="ui container">
+		{{template "base/alert" .ctxData}}
+	</div>
 	<div class="ui container admin-container">
 		{{template "admin/navbar" .ctxData}}
 		<div class="admin-main">
-			{{template "base/alert" .ctxData}}
 			{{/* block: admin-setting-content */}}
 
 {{if false}}{{/* to make html structure "likely" complete to prevent IDE warnings */}}