BR-DE-CVD-06-a: vehicle category without exactly one cva attribute

Add to every line with a CVD category exactly one cac:AdditionalItemProperty with cbc:Name cva and a permitted value, and remove duplicates. In CII the same applies to ram:ApplicableProductCharacteristic with ram:Description cva.

<cac:Item>
  <cbc:Name>City bus M3</cbc:Name>
  <cac:CommodityClassification>
    <cbc:ItemClassificationCode listID="CVD">M3</cbc:ItemClassificationCode>
  </cac:CommodityClassification>
</cac:Item>

<cac:Item>
  <cbc:Name>City bus M3</cbc:Name>
  <cac:CommodityClassification>
    <cbc:ItemClassificationCode listID="CVD">M3</cbc:ItemClassificationCode>
  </cac:CommodityClassification>
  <cac:AdditionalItemProperty>
    <cbc:Name>cva</cbc:Name>
    <cbc:Value>clean</cbc:Value>
  </cac:AdditionalItemProperty>
</cac:Item>

An invoice line carries a vehicle category with the scheme CVD, but the matching attribute cva is missing or appears more than once. The CVD extension requires both details as a pair in the same line: the category says what kind of vehicle it is, the attribute whether it is clean or zero-emission. Without the attribute the public body lacks the classification; with several attributes it would be contradictory. Per line: exactly one category, exactly one attribute.

• The attribute cva was set only in the first vehicle line, not in the following ones.
• The software writes the attribute twice, for example from master data and from the order.
• The classification was added but the attribute forgotten.