Provide a DELETE endpoint for white listing rules

[André Menneken]

Expected behavior

Rules should not actually be deleted, but the expiry date should be set.

Step needed

Add an endpoint, e.g. DELETE /api/whitelisting-rules/{id}?expiry_date=...
It should take an optional parameter expiry_date that defaults to now() and MUST not lie in the past.

Dependencies

[Michele Randi]

no more valid rule cannot be deleted.
expiry_date > now and the saved rule expiry_date > now