Add new methods to RegroupmentRepository and fix association

Regroupment/Center

src/Bundle/ChillMainBundle/Form/RegroupmentType.php

@@ -31,7 +31,7 @@ class RegroupmentType extends AbstractType
             ->add('centers', EntityType::class, [
                 'class' => Center::class,
                 'multiple' => true,
-                'attr' => ['class' => 'select2'],
+                'expanded' => true,
             ])
             ->add('isActive', CheckboxType::class, [
                 'label' => 'Actif ?',