Add an asynchronous Admin API endpoint [to redact all a user's events](https://element-hq.github.io/synapse/v1.116/admin_api/user_admin_api.html#redact-all-the-events-of-a-user),
and [an endpoint to check on the status of that redaction task](https://element-hq.github.io/synapse/v1.116/admin_api/user_admin_api.html#check-the-status-of-a-redaction-process).