Changes to List contact lists

added the non-success response with the status 429

added the optional property data/items/subscriber_description to the response with the 200 status

added the optional property data/items/public_description to the response with the 200 status

added the optional property data/items/subscribed_contacts_count to the response with the 200 status

added the optional property data/items/unsubscribed_contacts_count to the response with the 200 status