Scheduled auto back up

- [x] I am using the latest version of App Manager (F-Droid)
- [x] I have searched the issues and haven't found anything relevant
- [x] I have read the docs

**Is your feature request related to a problem? Please describe.**
I've many apps and live the life at limit, so I might occasionally loose all my data. Due to this, I've to do many backups manually from time to time, but I'd like to do this automatically.

**Describe the solution you'd like**
Just add an option to auto-backup selected apps in a list, how often should it be, etc.

**Describe alternatives you've considered**
By now, I'm just using LOS 17.1 default backup utility, which for some unknown reason to me it doesn't backup all apps (Edit: I read that some apps do not allow back ups, but fortunately AM does not care :smile:)