Duplicating an Agreement with Supplementary Documents does not duplicate the documents

Overview:
Steps to Reproduce:

1. Create an Agreement
2. Add a supplementary document
3. Duplicate the agreement
4. Check the identity / UUID of the supplementary document for the original agreement and for the duplicated agreement

Expected Results:

1. The supplementary document should be duplicated along with the agreement

Actual Results:

1. The same supplementary document is attached to the new agreement

Additional Information:
This means that updating the document on one of the agreements updates it on the other agreement
This also means that you cannot delete either supplementary document - because there is another Agreement linked to it which leads to an error when there is an attempt to delete the document from the agreement, or delete the agreement completely

I think this means that we not only need to fix the behaviour on duplication, but also fix any existing situations where two agreements point at the same document

Note that Licenses duplicates documents correctly when a license is duplicated - you end up with two licenses with two separate documents