Add Cart model, resource and its API, Pivot table with Items.

Update Items model to have relationship with cart.

app/Http/Resources/API/v2/CartResource.php

@@ -0,0 +1,28 @@
+<?php
+
+namespace App\Http\Resources\API\v2;
+
+use Illuminate\Http\Request;
+use Illuminate\Http\Resources\Json\JsonResource;
+
+class CartResource extends JsonResource
+{
+    /**
+     * Transform the resource into an array.
+     *
+     * @return array<string, mixed>
+     */
+    public function toArray(Request $request): array
+    {
+        $city_name = $this->city->name;
+        $company_name = $this->company->name;
+        $items = $this->items;
+
+        return [
+            'id' => $this->id,
+            'cityName' => $city_name,
+            'companyName' => $company_name,
+            'item' => new ItemCollection($items),
+        ];
+    }
+}