Change SimpleWorker::prepareTaskStrategy() to use Doctrine

This commit changes the method prepareTaskStrategy() in the class
SimpleWorker and all its child classes to use ScheduledTaskEntity
instead of ScheduledTask.

[MAILPOET-2996]

lib/Models/ScheduledTask.php

@@ -191,4 +191,16 @@ class ScheduledTask extends Model {
 
     return $query->findMany();
   }
+
+  // temporary function to convert an ScheduledTaskEntity object to ScheduledTask while we don't migrate the rest of
+  // the code in this class to use Doctrine entities
+  public static function getFromDoctrineEntity(ScheduledTaskEntity $doctrineTask): ?ScheduledTask {
+    $parisTask = self::findOne($doctrineTask->getId());
+
+    if (!$parisTask instanceof ScheduledTask) {
+      return null;
+    }
+
+    return $parisTask;
+  }
 }