ledger top up functionality and few small fixes for project architechture and design

frontend/pshared/lib/models/payment/operation_document.dart

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