[cherry-picked] abci++: add consensus parameter logic to control vote extension require height (#8547)

This PR makes vote extensions optional within Tendermint. A new ConsensusParams field, called ABCIParams.VoteExtensionsEnableHeight, has been added to toggle whether or not extensions should be enabled or disabled depending on the current height of the consensus engine. Related to: #8453

blocksync/pool.go

@@ -259,7 +259,7 @@ func (pool *BlockPool) AddBlock(peerID p2p.ID, block *types.Block, extCommit *ty
 	pool.mtx.Lock()
 	defer pool.mtx.Unlock()
 
-	if block.Height != extCommit.Height {
+	if extCommit != nil && block.Height != extCommit.Height {
 		return fmt.Errorf("heights don't match, not adding block (block height: %d, commit height: %d)", block.Height, extCommit.Height)
 	}
 
@@ -566,7 +566,9 @@ func (bpr *bpRequester) setBlock(block *types.Block, extCommit *types.ExtendedCo
 		return false
 	}
 	bpr.block = block
-	bpr.extCommit = extCommit
+	if extCommit != nil {
+		bpr.extCommit = extCommit
+	}
 	bpr.mtx.Unlock()
 
 	select {