feat: Implement data retention policy

- Replaced `data_storage.py` with `database.py` to use SQLite instead of a JSON file for data storage.
- Added an `enforce_retention_policy` function to `database.py` to delete data older than 7 days.
- Called this function in the main monitoring loop in `monitor_agent.py`.
- Added Docker container monitoring.
- Updated `.gitignore` to ignore `monitoring.db`.

.gitignore

@@ -1,6 +1,4 @@
-__pycache__/*
+*.pyc
 __pycache__/
-monitoring_data.json
-log_position.txt
-auth_log_position.txt
-monitoring_agent.log*
+.DS_Store
+monitoring.db