Add "numbers of backups to keep" for automatic-backups

[bf8392]

Is your feature request related to a problem? Please describe.
I've setted automatic-backups in a standard folder on every change. The problem is, that this feature keeps generating "endless" backups with every change. The other option (only backups on add totp) is not an option for me, as it will turn my restore-libary into a mess with outdated totp (because remove). As I sync with nextcloud, I can use multiple devices and absolutely love the solution! Thanks for all the development so far! :-)

Describe the solution you'd like
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Add an option with "numbers of backups to keep" so you don't throw various endless backups on storage

Describe alternatives you've considered
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Delete with external apps per task (unreliable and can lead to data-loss)

Additional context
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