Update the endpoint for the HubApp v6

Update the code to consider the changes to the structure of the JSON requests introduced by the Hub's v6.

* Replace the request `parameters` array of objects with key-value pairs
* Replace `number` keys with `id` for order and shipment
* Remove `message` fields and add `request_id` instead
* Replace the response `notifications` with `summary`

TODO:
* Fix specs (record vcr cassettes) - @peterberkenbosch ;)