code: func ClientOption(c ...option.ClientOption) broker.Option {
  	return func(o *broker.Options) {
  		if o.Context == nil {
  			o.Context = context.Background()
  		}
  		o.Context = context.WithValue(o.Context, clientOptionKey{}, c)
  	}
  }
docs: // ClientOption is a broker Option which allows google pubsub client options to be
  // set for the client