Opt contacts out of an SMS topic

Opt many contacts out of this topic in one call, as a background job: the contacts you list (contact_ids or emails, up to 1,000, each a contact of this workspace) or every member of a segment (segment_id, however many; also needs segments:read). Send exactly one. Each contact is opted out as Set a contact's topic preference would: one that was subscribed gets a topic.unsubscribed webhook and an activity row naming your key; one already opted out is left as it is, with no webhook. Suppressions and other topics are untouched, and there is no bulk opt-in. Listed contacts are checked first: the first that isn't one of yours is a 404 naming it (details), and nothing starts. The answer is the job (202, Location); follow it with Retrieve a job. Pass an Idempotency-Key so a retry answers the same job instead of starting another. An email topic's id is a 404 here. Requires the topics:write capability.