As fetching content data from the content property in TaxonomyEntry domain object is expensive (it's a proxy object as of now), we could at least add the contentId property.

Steps to reproduce:

1. Add a new Tag to Tags taxonomy.
2. Create a new simple Controller with the following code:

   <?php
   
   namespace App\Controller;
   
   use Ibexa\Contracts\Taxonomy\Service\TaxonomyServiceInterface;
   use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
   use Symfony\Component\HttpFoundation\Response;
   
   class TestController extends AbstractController
   {
       public function __construct(
           private readonly TaxonomyServiceInterface $service
       ) {
       }
   
       public function index(): Response
       {
           foreach($this->service->loadAllEntries('tags') as $entry) {
               dump($entry);
           }
           
           return new Response();
       }
   }
   

   "routes.yaml"

   index:
       path: /test
       controller: App\Controller\TestController::index
   

3. Access /test URI.

Result:
One is presented with a dumped Taxonomy Entry entity without contentId property.

Expected result:
It would be ideal if one is presented with a dumped Taxonomy Entry entity with contentId property.