Support Open Archiefbeheer destruction in Objects API

[CharString]

1. Be able to recognize when a Zaak is linked, in an unambiguous way.
2. Send nl.overheid.zaken.zaak-gelinkt events after successful POSTs that link something in the registry to a Zaak.
3. Add query_param to DELETE zaak: URI, response
   204 when gone
   200 when unlinked

See open-zaak/open-zaak#2251

REVISITED: SEE maykinmedia/open-klant#544