api/add_forge_now: Allow to use requests list endpoint with datatables
datatables is the javascript library we use on the frontend side to
display interactive tables.
As we use server-side processing, table data must be provided in a
paginated way by an HTTP endpoint.
Response format expected by datatables is different from the one
returned by the Web API endpoint listing add-forge requests.
So adapt the response format of that endpoint when we know the
input request has been sent by datatables.