🗃️(backend) make document/template creation atomic

When creating a new document/template via the API, we add the
logged-in user as owner of the created object. This should be
done atomically with the object creation to make sure we don't
end-up with an orphan object that the creator can't access
anymore.

src/backend/core/tests/documents/test_api_documents_trashbin.py

@@ -85,6 +85,7 @@ def test_api_documents_trashbin_format():
             "media_auth": True,
             "move": False,  # Can't move a deleted document
             "partial_update": True,
+            "restore": True,
             "retrieve": True,
             "update": True,
             "versions_destroy": True,