Bulk-unsubscribe a collection of contacts from email. The action runs asynchronously — poll the returned record with GET /api/v2/contacts/unsubscribe_actions/{id} to track progress via target_count and performed_count.
Exactly one target selection must be supplied: stable_id, stored_filter_id (alias filter_id), target_ids, or target_all. Returns 422 if none is provided or if the supplied value is invalid.