[ECOM-446] Add custom response for `OrderHeaderService`
The Order Header service in CBS, as defined in the Excel spreadsheet, returns three things: a "status", a message, and an order number. This PR adds a custom response object for the OrderHeaderService
defining those return values.
"Status" is defined as a VARCHAR so I'm making the assumption that it is distinct from 'success', which the AbstractServiceResponse
already provides. If they serve the same purpose, it can easily be removed.
Please review: @ahoffmann @weizhong-wang @lloyd-carter