it would be great to have a way to edit an ArchiveType once created, for example to insert/remove extensions, or tweak the description, or modify the compression_type value.

Ideally this would also implement the concept from #3976 and ensure some extension uniqueness -- though this already seems to exist, looking at kojihub.py https://pagure.io/koji/blob/master/f/kojihub/kojihub.py#_7957