Backup frequency setting

Is your feature request related to a problem? Please describe.
Thank you very much for implementing automatic backups ! Although this is undeniably a must-have and very welcome feature, I remain a bit frustrated by the rigidity of the chosen implementation :

I [...] have implemented a regular backup, keeping backups of

* every day for the past 7 days

* every Monday for the past 5 weeks

* every first Monday for the past 6 months

Describe the solution you'd like
Would it be possible to add an option to set the backup frequency ? Maybe this will have to wait for #1798 to be solved, in which case I suggest the following.

Describe alternatives you've considered
As a simpler alternative, letting the user set a cap for the number of generated backup files would fit a lot of use cases, I believe.

Additional context
Related to #1798, whose outcome might influence this issue.

No file, test, or entry point is named in the issue. Start by reading the existing automatic-backup implementation and related issue #1798, then determine whether the accepted scope is configurable frequency, a cap on generated backup files, or both; done requires an agreed behavior and tests for the selected setting.