#4586 Audit OAuth client deletion

Follow-up to #4498, part of #4459.

Problem

#4498 audits rotating an OAuth client's secret, with who did it and which choice they made. Deleting a client isn't audited, though it does more: it ends every serve link through that client, along with its tokens and consents.

Scope

• Audit client deletion in the same audit log #4498 uses, with the actor, the client, whether it was forced while in use, and how many links, tokens and consents ended.
• Never record a secret.
• Cover the browser and the API (DELETE /api/v1/collectives/{slug}/oauth-clients/{id}) alike.

Done when

• Deleting a client through either path writes one audit record with those fields.
• The erasure test #4498 added covers these records too.