feat: refactor staffing status assignment and filtering

src/Form/AssignmentFilterType.php

@@ -65,10 +65,10 @@ class AssignmentFilterType extends AbstractType
         ;
 
         if ($this->security->isGranted('ROLE_ADMINISTRATIVE')) {
-            $builder->add('status', ChoiceType::class, [
+            $builder->add('status', MultiselectType::class, [
                 'label' => 'Status',
                 'required' => false,
-                'placeholder' => 'nicht filtern',
+                'empty_label' => 'nicht filtern',
                 'choices' => [
                     'voll besetzt' => Assignment::STATUS_STAFFED,
                     'teilweise besetzt' => Assignment::STATUS_PARTLY_STAFFED,