Implement hook to manipulate the fields send to datatrans

With the current solution it is not possible without updating the module, to adjust the fields and their values in the request to Datatrans.
For example, we are currently missing a uppReturnMaskedCC field set to "yes" in the request to Datatrans. Without this field the masked credit card number is not returned in the request. In our case we need this masked credit card number.

With a hook we could adjust the fields which are being sent to datatrans, and thus add this field we need in our case.