Make getApiV1BoxesP1 optionally return unconfirmed boxes

getApiV1BoxesP1 returns box information, but there doesn't seem to be a way to make it return information for unconfirmed boxes. Only way to retrieve box information for unconfirmed boxes is to request the whole mempool, which is over the top when the box id is already known.
I suggest we add a `includeMempool` parameter to getApiV1BoxesP1 which, when set to true, also returns unconfirmed boxes when available for the given id.