feat: always allow twofactor apps

[st3iny]

Ref #149 (comment)
Ref #1249

Problem

A guest user will not be able to set up their second factor authentication method by default, e.g. TOTP and Webauthn. Admins have to specifically add the corresponding twofactor_* apps to the white list first.

Instead, attempting to enable, disable a second factor method or generating backup codes as a user will yield a cryptic internal server error response with no context. However, if a method is set up and the app is removed from the white list, the login will still work.

How to reproduce?

1. Create a guest user.
2. Install at least one twofactor app, e.g. twofactor_totp.
3. Enable the app white list for guest users and remove twofactor_totp from it.
4. Log in as the guest user.
5. Try to set up TOTP.

Observe 500 Internal Server Error responses.

Solution

Allow supported twofactor apps by default:

• twofactor_webauthn
• twofactor_totp
• twofactor_backupcodes
• twofactor_nextcloud_notifications