code: func DeduplicationFunction(dedup StringFromMessageFunc) broker.Option {
  	return func(o *broker.Options) {
  		if o.Context == nil {
  			o.Context = context.Background()
  		}
  		o.Context = context.WithValue(o.Context, dedupFunctionKey{}, dedup)
  	}
  }
docs: // DeduplicationFunction sets the function used to create the deduplication string
  // for a given message