code: func GetLastConfigIndexFromBlock(block *cb.Block) (uint64, error) {
  	md, err := GetMetadataFromBlock(block, cb.BlockMetadataIndex_LAST_CONFIG)
  	if err != nil {
  		return 0, err
  	}
  	lc := &cb.LastConfig{}
  	err = proto.Unmarshal(md.Value, lc)
  	if err != nil {
  		return 0, errors.Wrap(err, "error unmarshaling LastConfig")
  	}
  	return lc.Index, nil
  }
docs: // GetLastConfigIndexFromBlock retrieves the index of the last config block as
  // encoded in the block metadata