Implement backup retention options

[linesquarecube]

Checklist

• [X] I made sure that there are no existing issues - open or closed - to which I could contribute my information.
• [X] I made sure that there are no existing discussions - open or closed - to which I could contribute my information.
• [X] I have read the FAQs inside the app (Menu -> About -> FAQs) and my problem isn't listed.
• [X] I have taken the time to fill in all the required details. I understand that the bug report will be dismissed otherwise.
• [X] This issue contains only one feature request.
• [X] I have read and understood the contribution guidelines.
• [X] I optionally donated to support the Fossify mission.

Feature description

Implement a flexible backup retention system that allows users to control the timespan or quantity of automatic backups

Why do you want this feature?

As a user, I want to limit the number of backup files or set a retention period for backups because:

1. I currently have 215 .json backup files created at irregular intervals.
2. This large number of files reduces overview and organization.
3. It unnecessarily consumes storage space on my phone.
4. A limit of 3 to 5 backup files or a one-week retention period would be sufficient for my needs.

This feature would help me maintain a manageable number of backups while ensuring efficient use of my phone's storage.

Additional information

No response