call otp_login on registering passkey

[AlmerCarbonEquity]

I believe otp_login should be called when a passkey is added so that the user is thereafter authenticated with 2fa, just like how it is called on login. This is also how other packages like django-two-factor-auth do it. Otherwise we have to wait for a user to logout and then login again (with their passkey!) before they can see certain content.

[Stormheg]

I'm sure I had some reason not to initially, but I can't recall my reason anymore. It's probably not an important reason, given many other packages do.

Feel free to open a pull request with this change 👍