nip-9: deletation (with filters).

[kehiy]

No description provided.

[ZigBalthazar]

When the parent event does not exist, the children are useless and can cascade. It is better to delete all associated entities of an event that requests deletion. As this can involve many entities, it's better to carry out the deletion process asynchronously. This can be achieved using a job queue or job scheduler, etc, which will execute the deletion request when the system load is low.Sidecar pattern maybe useful.
admin should be able to force delete request manually out of queue, by management API but he can not cancel it.