Missing values in ACHField metadata for IAT

[dbenoff]

VF is a legal value for foreignExchangeIndicator in IATBatchHeader MTE and POS are legal values for transactionTypeCode in FirstIATAddendaRecord

https://www.bmocm.com/products/treasury/cashmanagement/iat/resource/images/IAT_Specific_Data.pdf

[afrunt]

@dbenoff prepare PR and I will add changes to next version. Thanks!