Changes to List forms

added the non-success response with the status 429

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

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

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

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

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

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

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

the response property data/items/title became required for the status 200

added the required property data/items/lists to the response with the 200 status