Redirect to Almost there page when inactive after signing up

For !24371 (merged) the soft_email_confirmation feature flag was removed and the implementation for the RegistrationsController#after_inactive_sign_up_path_for method was changed.

With the current settings, this method would never be called, because it is only called when user.active_for_authentication? (a Devise method from the confirmable module) is false after signing up. This is the case when:

• Gitlab::CurrentSettings.send_user_confirmation_email is true AND
• Devise's allow_unconfirmed_access_for is not set, or set to 0

In that case the user should be redirected to the "Almost there" page.

With the current Devise setting for allow_unconfirmed_access_for in config/initializers/8_devise.rb (30 days), that method is never called, but it is better to leave it in place because in the future this setting might be set to 0 again.

This MR restores that method's implementation to the original users_almost_there_path.

#201893 (closed)