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

app/models/form/admin_settings.rb

@@ -37,6 +37,8 @@ class Form::AdminSettings
     status_page_url
     captcha_enabled
     authorized_fetch
+    app_icon
+    favicon
   ).freeze
 
   INTEGER_KEYS = %i(
@@ -63,6 +65,8 @@ class Form::AdminSettings
   UPLOAD_KEYS = %i(
     thumbnail
     mascot
+    app_icon
+    favicon
   ).freeze
 
   OVERRIDEN_SETTINGS = {