models: move html_data_attributes to policies.

Move html_data_attributes definitions from models to policies. Which
attributes are permitted as data-* attributes is a view level concern
and should be defined on the policy level, not the model level. Models
should be agnostic about how they're used in views.

app/policies/ip_address_policy.rb

@@ -2,4 +2,8 @@ class IpAddressPolicy < ApplicationPolicy
   def index?
     user.is_moderator?
   end
+
+  def html_data_attributes
+    super & attributes.keys.map(&:to_sym)
+  end
 end