Update Message structure: change Payload type to bytes and add Encoding field

services/data_service/internal/domain/message.go

@@ -1,6 +1,14 @@
 package domain
 
+type Encoding string
+
+const (
+	EncodingJSON     Encoding = "json"
+	EncodingProtobuf Encoding = "protobuf"
+)
+
 type Message struct {
 	Identifier Identifier
-	Payload    any
+	Payload    []byte
+	Encoding   Encoding
 }