handle slugs in persistent data manager

src/Interfaces/PersistentData/IPersistentDataManager.php

@@ -12,6 +12,8 @@ interface IPersistentDataManager
 
     public function selectFromDbById($id, string $type, bool $useRelations = false, array $withRelations = []);
 
+    public function selectFromDbBySlug(string $slug, string $type, bool $useRelations = false, array $withRelations = []);
+
     public function loadRelationsFromDb(Model $model, bool $recursive = false, array $withRelations = []): void;
 
     public function saveToDb(Model $model): void;