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>

web_src/css/admin.css

@@ -1,4 +1,5 @@
 .admin-container {
+  margin-top: 15px;
   display: flex !important;
   gap: 16px;
 }