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.

prisma/migrations/20251206102601_init/migration.sql

@@ -0,0 +1,10 @@
+/*
+  Warnings:
+
+  - You are about to drop the column `metaData` on the `Products` table. All the data in the column will be lost.
+  - You are about to drop the column `productType` on the `Products` table. All the data in the column will be lost.
+
+*/
+-- AlterTable
+ALTER TABLE `Products` DROP COLUMN `metaData`,
+    DROP COLUMN `productType`;