convert report to json

Signed-off-by: Sebastian Schüpbach <sebastian.schuepbach@unibas.ch>

src/main/kotlin/KafkaTopology.kt

@@ -65,7 +65,7 @@ class KafkaTopology(private val settings: SettingsLoader) {
                     key,
                     ReportStatus.failure,
                     "Can't create model. Is there anything wrong with the data?"
-                )
+                ).toJson()
             }
             .to(reportingTopic)