updated document upload according to fresh api

frontend/pweb/lib/models/documents/operation.dart

@@ -1,9 +1,9 @@
 class OperationDocumentRequestModel {
-  final String paymentRef;
+  final String gatewayService;
   final String operationRef;
 
   const OperationDocumentRequestModel({
-    required this.paymentRef,
+    required this.gatewayService,
     required this.operationRef,
   });
-}
+}

frontend/pweb/lib/models/report/operation/document.dart

@@ -0,0 +1,9 @@
+class OperationDocumentInfo {
+  final String operationRef;
+  final String gatewayService;
+
+  const OperationDocumentInfo({
+    required this.operationRef,
+    required this.gatewayService,
+  });
+}