[Feature Request] A way to backup downloaded books and their progress

[PieSeek]

Checklist

• This issue contains only one feature request. I will open one issue for every feature I want to request.
• I checked, but didn't find any duplicates (open OR closed) of this issue in the repo.
• This feature is merely an UI/UX update.
• This feature is not going to conflict with many of the existing features/options.

Is your feature request related to a problem? Please describe.

It would be nice to backup books and their progress to Nextcloud or an external drive.

Describe the solution you'd like

An option in the settings to choose where to backup and how often (maybe even encrypted?).

How will you/everyone benefit from this feature?

Whenever you lose your phone or reinstall the app, your downloaded books and their progress would be saved so you could start reading where you left off.

Additional context

I don't think it's a high priority, though it would be a nice-to-have.

[PieSeek]

Oops, sorry. A duplicate of #147. Didn't notice it.