Introduce a new concept for the extra information stored in partial configs

In the HFC, we have a `PartialConsensus/LedgerConfig` that we can complete to a non-partial one using `EpochInfo Identity`. We're currently abusing this partial config to store *more* information than the non-partial one, i.e., hard-fork only information. For example, the hard-coded transition for Byron (`PartialLedgerConfig`) or the initial nonce for Shelley (`PartialConsensusConfig`). However, we pass the non-partial ones to the translation functions, which means we don't have access to the hard-fork only information from these configs, which would come in handy.

We should introduce a separate concept and type for this "hard-fork only information" that we currently store in the partial configs. We can then pass this type to the translation functions too, in addition to the non-partial configs. The partial config will now truly be partial again.