Failure to create valid transaction on minFeeA: 0 and minFeeB: 0

[matiwinnetou]

On Hydra, it is theoretically possible to run transactions completely for free.

In order to do this, protocol parameters which hydra node starts with have to have:

txFeeFixed = 0 txFeePerByte = 0

one of them is effectively minFeeA renamed and another one is minFeeB renamed.

Add support for zero fees Hydra transactions, currently for zero fees there is an error: "EmptyUTxO" or something like this.