Add stash-scheduler plugin

[dscisci]

Schedules automatic Stash library scans on an hourly, daily, or weekly basis at a user-specified time and timezone. Optionally runs an Identify task after each scan completes. Configured entirely through Stash's built-in plugin settings UI. No external dependencies beyond APScheduler.

Features
Schedule scans at hourly, daily, or weekly intervals
Configure the hour of day (and day of week for weekly)
Optionally run an Identify task automatically after each scan completes
Identify is skipped safely if the scan fails, is cancelled, or no job ID is returned
Run Now task for instant manual trigger (useful for testing)
Auto-start on system boot via systemd, Windows startup, or a cron job
All settings managed through Stash's built-in plugin settings UI — no config files to edit

This is an alternative to using something like filemonitor which is tricky to get setup and working on docker based systems

I've successfully tested used this on an Unraid stash setup