Feature/add cron in firefly iii

This is a feature to add automation. I've added the cron like suggested in the doccumentation.

It's currently in WIP just waiting another day to confirm the last modification work.
All good, I confirm that it's working correctly on my side.

It also solve issue #755

Summary by CodeRabbit

• New Features
  • Introduced an automated scheduled task service that performs a daily operation at 3 AM with timezone awareness.
  • Added a new service for cron jobs to improve task management.
  • Expanded configuration options with a new entry for cron version.
  • Added a new environment variable for enhanced security in the app service.