Add RegroupmentRepositoryInterface and integrate it

Created a new `RegroupmentRepositoryInterface` to define repository methods for Regroupment entities. Updated `RegroupmentRepository` to implement this interface, and replaced its usage in `ExportConfigNormalizer` for better abstraction and testability.

src/Bundle/ChillMainBundle/Repository/RegroupmentRepositoryInterface.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Chill\MainBundle\Repository;
+
+use Chill\MainBundle\Entity\Regroupment;
+use Doctrine\ORM\NonUniqueResultException;
+use Doctrine\ORM\NoResultException;
+use Doctrine\Persistence\ObjectRepository;
+
+/**
+ * @template-extends ObjectRepository<Regroupment>
+ */
+interface RegroupmentRepositoryInterface extends ObjectRepository
+{
+    /**
+     * @throws NonUniqueResultException
+     * @throws NoResultException
+     */
+    public function findOneByName(string $name): ?Regroupment;
+
+    /**
+     * @return array<Regroupment>
+     */
+    public function findRegroupmentAssociatedToNoCenter(): array;
+}