[FIX] Initialize `runs` list in `KubeflowRunResponse` to prevent null issues

src/main/java/kr/re/etri/autoflow/payload/response/KubeflowRunResponse.java

@@ -7,6 +7,6 @@ import java.util.List;
 
 @Data
 public class KubeflowRunResponse {
-    private List<KubeflowRunRequest> runs;
+    private List<KubeflowRunRequest> runs = new java.util.ArrayList<>();
     private int totalSize;
 }