New DatasetSet model

closes #1712 (closed)

TODO:

• create process dataset issue
• create new API endpoints issue

arkindex/documents/migrations/0006_index_cleanup.py

@@ -57,7 +57,7 @@ class Migration(migrations.Migration):
                     ),
                 ),
             ],
-            # This can be removed by manage.py squashmigrations
+            # This can be removed by `arkindex squashmigrations`
             elidable=True,
         ),
     ]