SCORU: withdrawal type for Rollup Management Protocol

Extend Rollup Management Protocl with a withdrawal type. This is needed for the inclusion proofs in L1 for verifying the new management operation for withdrawals from L2 to L1. Roughly:

type withdrawal = {
  parameter_ty : Script_repr.lazy_expr;
  parameter : Script_repr.lazy_expr;
  entrypoint : Entrypoint.t;
  destination: Contract.t
}

type atomic_withdrawal_batch = withdrawal list