Hard fork combinator: Track entropy throughout the chain

This will be necessary if we need to pass entropy from one era to the next. Right now it seems that this is not a requirement, but if it is, we could do something akin to `PartialLedgerConfig`:

```haskell
newtype Entropy = Entropy ByteString

-- | Partial consensus config
--
-- Unlike 'HasPartialLedgerConfig', there is no explicit update function here;
-- this happens instead more indirectly by picking a suitable 'ValidateView'
-- for 'HardForkProtocol'.
class ( ConsensusProtocol p
, NoUnexpectedThunks (PartialConsensusConfig p)
) => HasPartialConsensusConfig p where
data PartialConsensusConfig p :: *

-- | Construct 'ConsensusConfig' from 'PartialConsensusConfig'
completeConsensusConfig :: EpochInfo Identity
-> Entropy
-> PartialConsensusConfig p -> ConsensusConfig p

```