We have validatePayerOperatorApprovalAndFunds for dataSetCreated with nice error types. We need the same for piecesAdded to validate that we have enough funds to cover the new lockup for the data set according to the leaf count of that data set. As per #350 we don't have leaf count there, but we can get it from PDPVerifier and do the same calculation as is done in updatePaymentRates to work out the new rate and the new 30 day lockup amount from that and see that the user has funds, and if not, give a nice error.