[F-r] Adapt Legacy Backup from google drive backup

[Palloxin]

Describe your suggested feature

Make Legacy Backup work again WITH the full backup of the app like google drive.

Why

I want the comfortable offline version for obvious reasons. I cant use the google drive one because I de-googled my phone.

Other details

The dev that made the google drive version said he'll leave the adaptation of Legacy Backup to someone else.
So either someone else picks it or nobody else will.

Acknowledgements

• I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open or closed issue.
• I have written a short but informative title.
• If this is an issue with a source, I should be opening an issue in the sources repository.
• I have updated the app to version 2.0.0.
• I will fill out all of the requested information in this form.