This work will require definition of the DijkstraBlockBody type that will include an optional field with StrictMaybe PerasCert

It will also need a DijkstraEraBlockBody type class that will provide access to such certificate in an era agnostic manner.

Initially we don't need to pull in the PerasCert type from cardano-base and we can create a place holder type in Cardano.Ledger.BaseTypes for the time being