Update log retention period to 30 days in custom logger and add comment on log cleanup mechanism.

logs/custom_logger.py

@@ -19,6 +19,6 @@ filename = f'{current_dir}/helper_bot_{today}.log'
 logger.add(
     filename,
     rotation="00:00",
-    retention="5 days",
+    retention="30 days",
     format="{time:YYYY-MM-DD at HH:mm:ss} | {level} | {name} | {line} | {message}",
 )