create carrier files

controller, entity, repository, creation use case and corresponding
request dto

src/Carrier/UseCases/CreateCarrier.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace FreightQuote\Carrier\UseCases;
+
+use FreightQuote\Carrier\Carrier;
+use FreightQuote\Carrier\CarrierRepository;
+
+class CreateCarrier
+{
+    public function __construct(
+        private CreateCarrierRequest $dto,
+        private CarrierRepository $carrierRepo,
+    ) {}
+
+    public function execute(): Carrier
+    {
+        $carrier = new Carrier($this->dto->id, $this->dto->email);
+
+        return $this->carrierRepo->save($carrier); 
+    }
+}