[FEATURE] Background daemon process for reminders instead of one-time job

[pilosus]

Now scheduled tasks (reminders) work as a one-time jobs. It was desinged with the external crontab in mind. Some cloud providers lack cron jobs. That's why having a worker background process for scheduled reminders can be a good workaround.

We can implement it with the Java daemon threads. We can keep the existing one-time job solution and simply add an extra entypoint like:

java -jar app.jar --mode schedule-daemon