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/product-variants/dto/update-product-variant.dto.ts

@@ -0,0 +1,63 @@
+import { Type } from 'class-transformer'
+import { IsBoolean, IsInt, IsOptional, IsString } from 'class-validator'
+
+export class UpdateProductVariantDto {
+  @IsOptional()
+  @IsString()
+  name?: string
+
+  @IsOptional()
+  @IsString()
+  description?: string
+
+  @IsOptional()
+  @IsString()
+  sku?: string
+
+  @IsOptional()
+  @IsString()
+  barcode?: string
+
+  @IsOptional()
+  @IsString()
+  imageUrl?: string
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  attachmentId?: number
+
+  @IsOptional()
+  @IsString()
+  unit?: string
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  discount?: number
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  quantity?: number
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  alertQuantity?: number
+
+  @IsOptional()
+  @Type(() => Boolean)
+  @IsBoolean()
+  isActive?: boolean
+
+  @IsOptional()
+  @Type(() => Boolean)
+  @IsBoolean()
+  isFeatured?: boolean
+
+  @IsOptional()
+  @Type(() => Number)
+  @IsInt()
+  productId?: number
+}