See #16943

* Add tests

* Add security-related tests

My first (unpublished) attempt at fixing the issues introduced (extremely
hard-to-exploit) security vulnerabilities, addressing them in a test.

* Fix authentication failures after going halfway through a sign-in attempt

* Refactor `authenticate_with_sign_in_token` and `authenticate_with_two_factor` to make the two authentication steps more obvious

If someone tries logging in to an account and is prompted for a 2FA
code or sign-in token, even if the account's password or e-mail is
updated in the meantime, the session will show the prompt and allow
the login process to complete with a valid 2FA code or sign-in token

* feat: add possibility of adding WebAuthn security keys to use as 2FA

This adds a basic UI for enabling WebAuthn 2FA. We did a little refactor
to the Settings page for editing the 2FA methods – now it will list the
methods that are available to the user (TOTP and WebAuthn) and from
there they'll be able to add or remove any of them.
Also, it's worth mentioning that for enabling WebAuthn it's required to
have TOTP enabled, so the first time that you go to the 2FA Settings
page, you'll be asked to set it up.
This work was inspired by the one donde by Github in their platform, and
despite it could be approached in different ways, we decided to go with
this one given that we feel that this gives a great UX.

Co-authored-by: Facundo Padula <facundo.padula@cedarcode.com>

* feat: add request for WebAuthn as second factor at login if enabled

This commits adds the feature for using WebAuthn as a second factor for
login when enabled.
If users have WebAuthn enabled, now a page requesting for the use of a
WebAuthn credential for log in will appear, although a link redirecting
to the old page for logging in using a two-factor code will also be
present.

Co-authored-by: Facundo Padula <facundo.padula@cedarcode.com>

* feat: add possibility of deleting WebAuthn Credentials

Co-authored-by: Facundo Padula <facundo.padula@cedarcode.com>

* feat: disable WebAuthn when an Admin disables 2FA for a user

Co-authored-by: Facundo Padula <facundo.padula@cedarcode.com>

* feat: remove ability to disable TOTP leaving only WebAuthn as 2FA

Following examples form other platforms like Github, we decided to make
Webauthn 2FA secondary to 2FA with TOTP, so that we removed the
possibility of removing TOTP authentication only, leaving users with
just WEbAuthn as 2FA. Instead, users will have to click on 'Disable 2FA'
in order to remove second factor auth.
The reason for WebAuthn being secondary to TOPT is that in that way,
users will still be able to log in using their code from their phone's
application if they don't have their security keys with them – or maybe
even lost them.

* We had to change a little the flow for setting up TOTP, given that now
  it's possible to setting up again if you already had TOTP, in order to
  let users modify their authenticator app – given that now it's not
  possible for them to disable TOTP and set it up again with another
  authenticator app.
  So, basically, now instead of storing the new `otp_secret` in the
  user, we store it in the session until the process of set up is
  finished.
  This was because, as it was before, when users clicked on 'Edit' in
  the new two-factor methods lists page, but then went back without
  finishing the flow, their `otp_secret` had been changed therefore
  invalidating their previous authenticator app, making them unable to
  log in again using TOTP.

Co-authored-by: Facundo Padula <facundo.padula@cedarcode.com>

* refactor: fix eslint errors

The PR build was failing given that linting returning some errors.
This commit attempts to fix them.

* refactor: normalize i18n translations

The build was failing given that i18n translations files were not
normalized.
This commits fixes that.

* refactor: avoid having the webauthn gem locked to a specific version

* refactor: use symbols for routes without '/'

* refactor: avoid sending webauthn disabled email when 2FA is disabled

When an admins disable 2FA for users, we were sending two mails
to them, one notifying that 2FA was disabled and the other to notify
that WebAuthn was disabled.
As the second one is redundant since the first email includes it, we can
remove it and send just one email to users.

* refactor: avoid creating new env variable for webauthn_origin config

* refactor: improve flash error messages for webauthn pages

Co-authored-by: Facundo Padula <facundo.padula@cedarcode.com>