Rethink configuration

At the moment, we distinguish between `ConsensusConfig`, `BlockConfig` and `LedgerConfig`; however, it is not very clear what the boundaries are between these various bits of configuration. Moreover, as of https://github.com/input-output-hk/ouroboros-network/pull/2088 (which moved the era parameters from the block config to the ledger config), ledger tests now need to pass information around (era parameters) that they don't actually make any use of. We should rethink this design in such a way that the boundaries are very clear and the tests are only given the information that they need and nothing else.