feat: add product variant management functionality

- Implemented CreateProductVariantDto and UpdateProductVariantDto for product variant data transfer.
- Developed ProductVariantsController to handle CRUD operations for product variants.
- Created ProductVariantsService to interact with the database using Prisma.
- Added ProductVariantsModule to encapsulate the product variant feature.
- Included response mapping for consistent API responses.

src/generated/prisma/client.ts

@@ -47,16 +47,16 @@ export type User = Prisma.UserModel
  * 
  */
 export type Role = Prisma.RoleModel
+/**
+ * Model ProductVariant
+ * 
+ */
+export type ProductVariant = Prisma.ProductVariantModel
 /**
  * Model Product
  * 
  */
 export type Product = Prisma.ProductModel
-/**
- * Model ProductInfo
- * 
- */
-export type ProductInfo = Prisma.ProductInfoModel
 /**
  * Model ProductBrand
  *