Capture audit events for related models when deleting the parent

If you delete a model that has related models which are also audited, only the parent model will have an audit event created.

Here's how we worked around this:
https://github.com/dimagi/open-chat-studio/blob/f7e86efe5e15921b2c9de4f476ffe719d10ed62b/apps/utils/deletion.py#L9-L32