Andotp: Support automatic backup with OpenPGP key

[dohseven]

Is your feature request related to a problem? Please describe.
According to the FAQ, it's already possible to automatically backup new entries, but only if a backup password is set. However I use the OpenPGP encryption for my backups, not the password one, and therefore I'm unable to use this feature.

Describe the solution you'd like
It would be great to be able to enable this feature if an OpenPGP key is selected in the settings, along with the two other options described in the FAQ (append date to filename and backup directory selected).

Describe alternatives you've considered
None

[flocke]

This is probably not going to happen anytime soon. andOTP uses OpenKeychain for PGP encryption and as far as I know they don't support encryption in the background without user interaction. But I will keep an eye on it and implement it as soon as possible.