Refactored code to use PHP8 attributes instead of annotations

In this change, Doctrine and validation annotations have been replaced with PHP8 Attributes. The Rector tool has been configured with a list of annotations to convert to attributes. As a consequence, the PHPStan's rules have been updated to reflect these changes. The PHP8's nullable operator (?) has been added where required, and comments in field declaration have been replaced with #[Attribute] syntax.

src/Bundle/ChillMainBundle/Workflow/Validator/EntityWorkflowCreation.php

@@ -17,9 +17,8 @@ namespace Chill\MainBundle\Workflow\Validator;
  * * a handler exists;
  * * a related entity does exists;
  * * a workflow can be associated with this entity.
- *
- * @Annotation
  */
+#[\Attribute(\Attribute::TARGET_CLASS)]
 class EntityWorkflowCreation extends \Symfony\Component\Validator\Constraint
 {
     public string $messageEntityNotFound = 'Related entity is not found';