Added entities config for domains

module/Core/src/Entity/Domain.php

@@ -0,0 +1,22 @@
+<?php
+declare(strict_types=1);
+
+namespace Shlinkio\Shlink\Core\Entity;
+
+use Shlinkio\Shlink\Common\Entity\AbstractEntity;
+
+class Domain extends AbstractEntity
+{
+    /** @var string */
+    private $authority;
+
+    public function __construct(string $authority)
+    {
+        $this->authority = $authority;
+    }
+
+    public function getAuthority(): string
+    {
+        return $this->authority;
+    }
+}