code: func (manager *Manager) GetTransactor(channel string, privateCredential, publicCredential []byte) (Transactor, error) {
  	ledger, err := manager.LedgerManager.GetLedgerReader(channel)
  	if err != nil {
  		return nil, errors.Wrapf(err, "failed getting ledger for channel: %s", channel)
  	}
  	return &plain.Transactor{Ledger: ledger, PublicCredential: publicCredential}, nil
  }
docs: // GetTransactor returns a Transactor bound to the passed channel and whose credential
  // is the tuple (privateCredential, publicCredential).