Feature/structured data weight and dimensions

[MaxBentz]

All changes meet the following requirements

• [ ] Changelog entry was added
• [ ] Changes have been documented
• [x] Changes have been tested by the author
• [ ] Changes have been tested by the reviewer

@plentymarkets/plentyshop

I added a conditional output for the values. In my opinion it's better to submit no data than wrong data. I changed the position of output because of the conditional output, so that there is no unnecessary comma at the end. I added the unitCode for the dimensions and weight.