Fix `webauthn_id` generated by `after_initialize` is never persisted for existing users

[santiagorodriguez96]

Our WebauthnAuthenticationGenerator injects webauthn logic to the user model, and as part of that logic, it generates an after_initialize callback that is used to set the webauthn_id:

webauthn-rails/lib/generators/webauthn_authentication/webauthn_authentication_generator.rb

Lines 164 to 182 in 1aca187

	def inject_webauthn_content_to_user_model
	inject_into_file "app/models/user.rb", after: "normalizes :email_address, with: ->(e) { e.strip.downcase }\n" do
	<<-RUBY.strip_heredoc.indent(2)
	has_many :webauthn_credentials, dependent: :destroy
	with_options class_name: "WebauthnCredential" do
	has_many :second_factor_webauthn_credentials, -> { second_factor }
	has_many :passkeys, -> { passkey }
	end
	after_initialize do
	self.webauthn_id ||= WebAuthn.generate_user_id
	end
	def second_factor_enabled?
	webauthn_credentials.any?
	end
	RUBY
	end

The problem is that this callback sets webauthn_id in memory on every model load, but for existing users who don't yet have a webauthn_id, the generated value is not saved to the database until the user is updated in some way. Until that happens, since no controller in the passkeys/security keys registration flow calls save on the user record, each request generates a different ephemeral value, which makes it so that the credentials are stored in the authenticators with different identifiers for the same user.