Password/PIN-protection and encryption option for notes (files)

[MiMoHo]

Is your feature request related to a problem? Please describe. As described in #695 notes are saved in files in the Nextcloud and are editable in other clients. As I may want to save sensitive data in notes, I prefer an option to encrypt and password- or pin-protect notes.

Describe the solution you'd like Save files as currently but with improved data management as suggested in #695 as well as give an option to password- or pin-protect one or all notes in the Notes app to give an extra security layer of protection and prevent other apps and clients from unauthorized access.

[bonswouar]

I'm totally in favor of having encryption options, although I don't think #695 would be needed as the notes content will be encrypted anyway