def build_promise(depending_job, param_key)
      Promise.new.tap do |promise|
        promise.assign_attributes(job_id: job.id, hash_field: param_key, result_key: result_key)
        depending_job.promise_ids << promise.id
      end
    end
def build_promise(depending_job, param_key)
      Promise.new.tap do |promise|
        promise.assign_attributes(job_id: job.id, hash_field: param_key, result_key: result_key)
        depending_job.promise_ids << promise.id
      end
    end
Builds promise from this future
 @api private
 @param depending_job [Conflow::Job] job which will use new promise
 @param param_key [Symbol, String] key in result hash that holds promised value
 @return [Conflow::Promise] promise object