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

Update Items model to have relationship with cart.

database/migrations/2023_06_15_134235_create_carts_table.php

@@ -0,0 +1,38 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::create('carts', function (Blueprint $table) {
+            $table->id();
+            $table->unsignedBiginteger('city_id')->unsigned();
+            $table->unsignedBiginteger('company_id')->unsigned();
+            $table->unsignedBiginteger('user_id')->unsigned();
+            $table->string('status'); // CART | DONE
+
+            $table->foreign('city_id')->references('id')
+                 ->on('cities')->onDelete('cascade');
+            $table->foreign('company_id')->references('id')
+                 ->on('companies')->onDelete('cascade');
+            $table->foreign('user_id')->references('id')
+                 ->on('users')->onDelete('cascade');
+            $table->timestamps();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('carts');
+    }
+};