Draft: Hugin-Munin test set clone command

Marking as draft since this isn't intended to be merged.

See https://redmine.teklia.com/issues/3595

Usage:

1. Create a corpus

2. arkindex clone 45ea1d87-0205-4bd3-9eb1-ee808025875a $CORPUS_ID
   arkindex clone 6955101b-2ec5-459e-9752-3b471d1c2ea1 $CORPUS_ID

3. ???
4. Profit