Allow any fee config

[tomt1664]

Extension of #1333

HasValidFee (called from CheckInputs) is a consensus check for each tx that

1. any fee output does not exceed MAX_MONEY
2. any fee output is not 0 value
3. the total fees for a tx do not exceed MAX_MONEY

Another check in CheckInputs checks that the total fees for a block do not exceed MAX_MONEY

To enable both zero fee outputs and for total block and tx fee outputs (and total fee outputs) to exceed MAX_MONEY (fee outputs can be issued assets in addition to pegged asset, which total supply can exceed MAX_MONEY) and new chain config option is added: -con_allow_any_fee

[jsarenik]

I would just like to note here that a zero fee raw tx worked for me fine on the unofficial liquidtestnet4 already some time ago. Not tested with any other assets back then.

See https://kitchen.anyone.eu.org/lt4/zero.txt - the tx is present in current lt4 blockchain. Confidential. No fee (Liquid "fee" structure empty).

[tomt1664]

I would just like to note here that a zero fee raw tx worked for me fine on the unofficial liquidtestnet4 already some time ago. Not tested with any other assets back then.

See https://kitchen.anyone.eu.org/lt4/zero.txt - the tx is present in current lt4 blockchain. Confidential. No fee (Liquid "fee" structure empty).

A transaction can have a zero fee if there is no fee output (e.g. this lt4 tx) - that is consensus valid. But it cannot include an explicit fee output that has zero value (gets checked here:

elements/src/confidential_validation.cpp

Line 33 in b379bb2

if (fee == 0 || !MoneyRange(fee))

).

[tomt1664]

I've updated #1333 so the wallet does not add a fee output if the fee is zero - this is valid in current consensus rules.

The PR - enabling any fee value - is relevant to using issued assets as fees. I'll leave it open in draft - it is unlikely to be useful before issuance beyond MAX_MONEY is also enabled.