static FlexibleBlockHashTerminalCondition blockHash(
      final Hash blockHash, final Blockchain blockchain) {
    return new FlexibleBlockHashTerminalCondition(blockHash, blockchain);
  }
When we want the full sync to finish on a target hash. For instance when we reach a merge
checkpoint.

@param blockHash target hash to look for
@param blockchain blockchain to reach the difficulty on
@return true when blockchain contains target hash (target hash can be changed)
ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/sync/fullsync/SyncTerminationCondition.java