It must not be possible to delete IONMedia items which are used in published pages (also consider usage via StreamField / IonMediaBlock)

[rollacting]

limiting this to published pages would be enough imho, since the validation is triggered when trying to publish drafts with missing video files

[rollacting]

also, can we add audit-log logic to our ION media / image models?
https://docs.wagtail.io/en/stable/advanced_topics/audit_log.html