Set response type and minor restructure

receiver/datadogreceiver/receiver.go

@@ -244,18 +244,21 @@ func (ddr *datadogReceiver) handleTraces(w http.ResponseWriter, req *http.Reques
 		}
 	}
 
+	responseBody := "OK"
+	contentType := "text/plain"
 	urlSplit := strings.Split(req.RequestURI, "/")
 	if len(urlSplit) == 3 {
 		// Match the response logic from dd-agent https://github.com/DataDog/datadog-agent/blob/86b2ae24f93941447a5bf0a2b6419caed77e76dd/pkg/trace/api/api.go#L511-L519
 		switch version := urlSplit[1]; version {
 		case "v0.1", "v0.2", "v0.3":
-			_, _ = w.Write([]byte("OK"))
+			// Keep the "OK" response for these versions
 		default:
-			_, _ = w.Write([]byte("{}"))
+			contentType = "application/json"
+			responseBody = "{}"
 		}
-	} else {
-		_, _ = w.Write([]byte("OK"))
 	}
+	w.Header().Set("Content-Type", contentType)
+	_, _ = w.Write([]byte(responseBody))
 }
 
 // handleV1Series handles the v1 series endpoint https://docs.datadoghq.com/api/latest/metrics/#submit-metrics