Asynchronously grant Job Admin roles on specific jobs to many users in a single call. Each item follows the same shape as POST /v3/user_job_permissions, with job_id, user_id, and role_id required, and is processed independently. A bulk_action_uuid is returned immediately. Per-item success or failure is reported through GET /v3/bulk_requests/{bulk_action_uuid}. Items whose user_id references a site admin create no permission row and are reported as successful with an empty result, since site admins already have access to every non-confidential job.