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.config.ts

@@ -1,14 +1,15 @@
 // This file was generated by Prisma and assumes you have installed the following:
 // npm install --save-dev prisma dotenv
-import "dotenv/config";
-import { defineConfig, env } from "prisma/config";
+import 'dotenv/config'
+import { defineConfig, env } from 'prisma/config'
 
 export default defineConfig({
-  schema: "prisma/schema.prisma",
+  schema: 'prisma/schema.prisma',
   migrations: {
-    path: "prisma/migrations",
+    path: 'prisma/migrations',
+    seed: 'tsx prisma/seed.ts',
   },
   datasource: {
-    url: env("DATABASE_URL"),
+    url: env('DATABASE_URL'),
   },
-});
+})