Add 'Optional' import to {{ cookiecutter.backend_package_name }}.py

adding 'Optional' import to avoid import errors

{{ cookiecutter.package_name }}/sigma/backends/{{ cookiecutter.backend_package_name }}/{{ cookiecutter.backend_package_name }}.py

@@ -6,7 +6,7 @@
 from sigma.pipelines.{{ cookiecutter.backend_package_name }} import # TODO: add pipeline imports or delete this line
 import sigma
 import re
-from typing import ClassVar, Dict, Tuple, Pattern, List, Any
+from typing import ClassVar, Dict, Tuple, Pattern, List, Any, Optional
 
 class {{ cookiecutter.backend_class_name }}(TextQueryBackend):
     """{{ cookiecutter.target_name }} backend."""
@@ -162,4 +162,4 @@ def finalize_output_{{ format }}(self, queries: List[str]) -> Any:
         # - list of dict: serialize each item as JSON and output all separated by newlines.
         return "\n".join(queries)
     {% endfor %}
-    {% endif %}
+    {% endif %}