Add new global setting to control auto-upload of test reports (#3137)

* Add new global setting to control auto-upload of test reports

* Adds callback to attach a copy of the test report when printing

* Fix for all attachment API endpoints

- The AttachmentMixin must come first!
- User was not being set, as the custom 'perform_create' function was never called

* Remove duplicated UserSerializer

* display uploading user in attachment table

* Add unit test to check the test report is automatically uploaded

InvenTree/stock/migrations/0071_auto_20211205_1733.py

@@ -20,9 +20,9 @@ def delete_scheduled(apps, schema_editor):
 
     items = StockItem.objects.filter(scheduled_for_deletion=True)
 
-    logger.info(f"Removing {items.count()} stock items scheduled for deletion")
-
-    items.delete()
+    if items.count() > 0:
+        logger.info(f"Removing {items.count()} stock items scheduled for deletion")
+        items.delete()
 
     Task = apps.get_model('django_q', 'schedule')