HardFork into a new era

[lehins]

Current implementation of Conway will successfully update the protocol version in the Params using HardForkInitiation governance action, which would probably be enough for an intra-era hardfork. The same can't be said about the protocol version update that initiates transition into a new era. The reason for this deficiency is that consensus HardFork combinator relies on internals of the ledger rules and logic of predicting the protocol version update, which has completely changed in Conway.

This needs to be fixed by removing this logic from consensus codebase and abstracting away in ledger in an era agnostic manner the question of: "what will be the protocol version on the next epoch boundary?"

Relevant Consensus ticket: IntersectMBO/ouroboros-consensus#920