support key publish option

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

kgo.go

@@ -247,9 +247,16 @@ func (k *kBroker) publish(ctx context.Context, msgs []*broker.Message, opts ...b
 	records := make([]*kgo.Record, 0, len(msgs))
 	var errs []string
 	var err error
+	var key []byte
+
+	if options.Context != nil {
+		if k, ok := options.Context.Value(publishKey{}).([]byte); ok && k != nil {
+			key = k
+		}
+	}
 
 	for _, msg := range msgs {
-		rec := &kgo.Record{}
+		rec := &kgo.Record{Key: key}
 		rec.Topic, _ = msg.Header.Get(metadata.HeaderTopic)
 		if options.BodyOnly {
 			rec.Value = msg.Body
@@ -273,6 +280,7 @@ func (k *kBroker) publish(ctx context.Context, msgs []*broker.Message, opts ...b
 			errs = append(errs, result.Err.Error())
 		}
 	}
+
 	if len(errs) > 0 {
 		return fmt.Errorf("publish error: %s", strings.Join(errs, "\n"))
 	}