store starting time of the proposal in its datum

... hardcoded to 0 upon creation for now

agora-sample/Sample/Shared.hs

@@ -37,6 +37,7 @@ module Sample.Shared (
   proposalValidatorHash,
   proposalValidatorAddress,
   proposalTimingConfig,
+  tmpProposalStartingTime,
 
   -- ** Authority
   authorityToken,
@@ -76,6 +77,7 @@ import Agora.Proposal (
   ProposalThresholds (..),
  )
 import Agora.Proposal.Time (
+  ProposalStartingTime (..),
   ProposalTimingConfig (..),
  )
 import Agora.Stake (Stake (..))
@@ -197,6 +199,10 @@ proposalTimingConfig =
     , executingTime = 3000
     }
 
+-- FIXME: should be removed.
+tmpProposalStartingTime :: ProposalStartingTime
+tmpProposalStartingTime = ProposalStartingTime 0
+
 ------------------------------------------------------------------
 
 treasuryOut :: TxOut