Introduce support for Genesis and big ledger peer snapshot data

[crocodile-dentist]

Genesis consensus mode is a new feature planned to begin from the Conway era. It's goal is the ensure that a bootstrapping node ends up on a good chain if the node talks to at least one honest peer. In a decentralized environment, big ledger peers are a proxy for honest actors. To enable connections to these peers that may not be yet available to the node based on its ledger state, a snapshot of these peers can be made available to the networking layer. New functionality is required to leverage this data:

• New consensus mode (Genesis)
• Support for serialization
• Changes to ledgerPeersProvider to pick and distribute peers from the snapshot to client code
• Exposing means of calculating big ledger peers to ouroboros-networking-api
• Tests