Customer Invoices new validation on rot/rut

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New validation error on POST /v2/customerinvoices - RotReducedInvoicingPropertyName

In order to fix a bug and align to the behaviour inside eAccounting the API will now return a 2000 - DataModelValidationError when using POST /v2/customerinvoices with a set RotPropertyType but empty RotReducedInvoicingPropertyName.