add unit tests for s3 enrich processor

Signed-off-by: Xun Zhang <xunzh@amazon.com>

Author: Zhangxunmt

data-prepper-plugins/s3-enrich-processor/src/main/java/org/opensearch/dataprepper/plugins/s3_enrich/processor/s3source/S3ObjectWorker.java

@@ -92,7 +92,7 @@ private void doProcessObject(final S3ObjectReference s3ObjectReference) throws E
                 try {
                     Event event = record.getData();
 
-                    String correlationValue = event.getJsonNode().get(s3EnricherProcessorConfig.getCorrelationKey()).asText();
+                    String correlationValue = event.getJsonNode().get(s3EnricherProcessorConfig.getCorrelationKeys().get(0)).asText();
 
                     event.getMetadata().setExternalOriginationTime(originationTime);
                     event.getEventHandle().setExternalOriginationTime(originationTime);