Task: Add sample client sdk

lib/sdk/services/CategoryService.dart

@@ -0,0 +1,7 @@
+import 'package:sample_dart_dsdk/sdk/models/CategoryModel.dart';
+
+class CategoryService {
+  List<Category> getAll() {
+    return List.empty();
+  }
+}

lib/sdk/services/ProductService.dart

@@ -0,0 +1,15 @@
+import 'package:sample_dart_dsdk/sdk/models/ProductModel.dart';
+
+class ProductService {
+  List<Product> getAll() {
+    return List.empty();
+  }
+
+  Product getOne() {
+    return Product.fromJson(null);
+  }
+
+  Product create() {
+    return Product.fromJson(null);
+  }
+}