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

Update Items model to have relationship with cart.

database/seeders/CartSeeder.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace Database\Seeders;
+
+use Illuminate\Database\Console\Seeds\WithoutModelEvents;
+use Illuminate\Database\Seeder;
+
+class CartSeeder extends Seeder
+{
+    /**
+     * Run the database seeds.
+     */
+    public function run(): void
+    {
+        //
+    }
+}