feat: update EventHandler and EventPublisher interfaces to include Channel and PublishTo methods

contracts/events.go

@@ -4,11 +4,15 @@ import "github.com/ThreeDotsLabs/watermill/message"
 
 type EventHandler interface {
 	Topic() string
-	PublishToTopic() string
+	Channel() Channel
+	PublishTo() (Channel, string)
 	Handler(msg *message.Message) ([]*message.Message, error)
 }
 
+type Channel string
+
 type EventPublisher interface {
 	Topic() string
+	Channel() Channel
 	Marshal() ([]byte, error)
 }