feat: Cause exception when using undefined variable

This is important to notice usage of links that do not exist

pad_initiator.py

 #!/usr/bin/env python3
 from typing import List, Dict, Optional, Tuple
 
-from jinja2 import Template
+from jinja2 import Template, StrictUndefined
 
 from os import environ, path, getcwd, makedirs
 from dotenv import load_dotenv
@@ -52,7 +52,7 @@ def templatePad(file_name: str, raw_data: str, links: Dict[str, str]) -> str:
     }
 
     try:
-        template = Template(source=raw_data, keep_trailing_newline=True)
+        template = Template(source=raw_data, keep_trailing_newline=True, undefined=StrictUndefined)
         return template.render(variables_for_template)
     except Exception as e:
         raise Exception(f"Failed to template for {file_name}.") from e