Allow admins to configure instance favicon and logo (#30040)

app/helpers/application_helper.rb

@@ -240,6 +240,13 @@ module ApplicationHelper
     EmojiFormatter.new(html, custom_emojis, other_options.merge(animate: prefers_autoplay?)).to_s
   end
 
+  def site_icon_path(type, size = '48')
+    icon = SiteUpload.find_by(var: type)
+    return nil unless icon
+
+    icon.file.url(size)
+  end
+
   private
 
   def storage_host_var