Bulk partial update of monitor-level properties for one or more monitors in a single request. Supports pausing/resuming (is_paused) and updating title, description, priority, sample limit, and notification channels. Check- and definition-level fields are not accepted here — use PATCH /check or PUT /monitor for those. Each item must include monitor_id and at least one updatable field; fields that are omitted are left unchanged. Notification channels use replace-on-present semantics: omit the field to leave channels untouched, send an empty array to clear them, or send a list to replace the set. Monitors in the request that do not exist are reported in the response's not_found list rather than failing the request.