Use <legend> tags to group radio button fields

In a few places, we were using <label> tags that pointed to elements
that didn't exist.

app/components/admin/site_customization/pages/form_component.rb

@@ -6,4 +6,10 @@ class Admin::SiteCustomization::Pages::FormComponent < ApplicationComponent
   def initialize(page)
     @page = page
   end
+
+  private
+
+    def attribute_name(attribute)
+      SiteCustomization::Page.human_attribute_name(attribute)
+    end
 end