Reimplement 2FA to create a smother user flow and add support for passkeys

[frjo]

Goals are:

• Make 2FA as smooth as possible for users. Especially important for organisations that enforce 2FA.
• Replace wizard multistep with, if possible, single page solution.
• Implement passkeys as a stand alone loggin method. The UI should encourage people to switch to it. (With passkeys no 2FA is needed even if enforced.)
• Allow for multiple passkeys.
• Allow users to remove their password.
• New 2FA should if possible not force people to reset their current 2FA codes.