PayloadId should be unique for each PayloadAttributes instance

[MarekM25]

ethereum/execution-apis#401
ethereum/pm#754 (comment)

Our PayloadId generation is not unique once only withdrawals are changed. It is a CL (Nimbus) bug, but it happened on besu<>nimbus so it might happen on Nethermind<>Nimbus as well. See the above links for more context

[LukaszRozmej]

Let's move ComputeNextPayloadId method to be under PayloadAttributes class, so in the future we won't miss that.