Enroll Consensus into the CIP mechanism

[dnadales]

We should define a process for proposing changes to Consensus to enable the community to contribute to the design and specification of new features. Such a process should be crystalized in the form of a CIP.

We can use the corresponding CIPs for Plutus and Ledger as inspiration.

The CIP should be submitted according to the process defined here.

• We also need to register the Consensus category in CIP-0001.