NewCommittee proposal needs more info

[lehins]

We need to add a set for the previous committee and the epoch number when the new committee member should expire. Also the key role needs fixing. So, instead of current

https://github.com/input-output-hk/cardano-ledger/blob/319f0f3e5bb9ee8411f059f72e31dcd30a92afc4/eras/conway/impl/src/Cardano/Ledger/Conway/Governance/Procedures.hs#L304

  | NewCommittee
    !(Set (Credential 'CommitteeCold (EraCrypto era))) -- Old Committee
    !(Map (Credential 'CommitteeCold (EraCrypto era)) EpochNo) -- New Committee with expiration
    !Rational -- Quorum