DivTree: Find by nodeKey

Accession filtering now allows for finding all Accession records that belong to some DiversityTree through DiversityTreeAccessionRef.

We would like to be able to list accessions that:

• Match the specified nodeKey "X.10.30" using .eq()
• or begin with the specified value using .startsWith("X.10.30.") Note the extra . at the end!

This filtering should only be supported when the tree filter is specified.

Part of #528 (closed).