* Update devise-two-factor to unreleased fork for Rails 6 support

Update tests to match new `rotp` version.

* Update nsa gem to unreleased fork for Rails 6 support

* Update rails to 6.1.3 and rails-i18n to 6.0

* Update to unreleased fork of pluck_each for Ruby 6 support

* Run "rails app:update"

* Add missing ActiveStorage config file

* Use config.ssl_options instead of removed ApplicationController#force_ssl

Disabled force_ssl-related tests as they do not seem to be easily testable
anymore.

* Fix nonce directives by removing Rails 5 specific monkey-patching

* Fix fixture_file_upload deprecation warning

* Fix yield-based test failing with Rails 6

* Use Rails 6's index_with when possible

* Use ActiveRecord::Cache::Store#delete_multi from Rails 6

This will yield better performances when deleting an account

* Disable Rails 6.1's automatic preload link headers

Since Rails 6.1, ActionView adds preload links for javascript files
in the Links header per default.

In our case, that will bloat headers too much and potentially cause
issues with reverse proxies. Furhermore, we don't need those links,
as we already output them as HTML link tags.

* Switch to Rails 6.0 default config

* Switch to Rails 6.1 default config

* Do not include autoload paths in the load path

* 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>

Fix #3961

Not a serious issue because they are meaningless past single use

* Add spec coverage for settings/two_factor_auth area

* extract setup method for qr code

* Move otp required check to before action

* Merge method only used once

* Remove duplicate view

* Consolidate creation of @codes for backup

* Move settings/2fq#recovery_codes to settings/recovery_codes#create

* Rename settings/two_factor_auth#disable to #destroy

* Add coverage for the otp required path on 2fa#show

* Clean up the recovery codes list styles

* Move settings/two_factor_auth to settings/two_factor_authentication

* Reorganize the settings two factor auth area

Updated to use a flow like:

- settings/two_factor_authentication goes to a #show view which has a button
  either enable or disable 2fa on the account
- the disable button turns off the otp requirement for the user
- the enable button cycles the user secret and redirects to a confirmation page
- the confirmation page is a #new view which shows the QR code for user
- that page posts to #create which verifies the code, and creates the recovery
  codes
- that create action shares a view with a recovery codes controller which can be
  used separately to reset codes if needed