Add icon field to instance endpoint (#30205)

app/helpers/instance_helper.rb

@@ -13,6 +13,22 @@ module InstanceHelper
     safe_join([description_prefix(invite), I18n.t('auth.description.suffix')], ' ')
   end
 
+  def instance_presenter
+    @instance_presenter ||= InstancePresenter.new
+  end
+
+  def favicon_path(size = '48')
+    instance_presenter.favicon&.file&.url(size)
+  end
+
+  def app_icon_path(size = '48')
+    instance_presenter.app_icon&.file&.url(size)
+  end
+
+  def use_mask_icon?
+    instance_presenter.app_icon.blank?
+  end
+
   private
 
   def description_prefix(invite)