[export] Add referrer on accompanying course filter between dates feature and relevant tests

Implemented a new filter to the software for social workers. This filter, ReferrerFilterBetweenDates, enables filtering of query results based on a range of dates and accepted referrers. Tests for this new functionality have also been added to ensure the feature works as expected.

src/Bundle/ChillPersonBundle/Export/Filter/AccompanyingCourseFilters/ReferrerFilterBetweenDates.php

@@ -30,7 +30,7 @@ use Symfony\Component\Form\FormBuilderInterface;
  *
  * @see ReferrerFilterBetweenDatesTest for tests
  */
-class ReferrerFilterBetweenDates implements FilterInterface
+final readonly class ReferrerFilterBetweenDates implements FilterInterface
 {
     private const A = 'acp_referrer_filter_uhistory';
 
@@ -40,7 +40,7 @@ class ReferrerFilterBetweenDates implements FilterInterface
     private const PU = 'acp_referrer_filter_users';
 
     public function __construct(
-        private readonly RollingDateConverterInterface $rollingDateConverter,
+        private RollingDateConverterInterface $rollingDateConverter,
         private UserRender $userRender
     ) {
     }