gen2 fix callout about verification email style, use auth resource de… (aws-amplify#6736)

* gen2 fix callout about verification email style, use auth resource definition

* immutable -> mutable

Author: josefaidt

src/pages/gen2/build-a-backend/auth/enable-sign-up/index.mdx

@@ -53,7 +53,7 @@ export const auth = defineAuth({
 + userAttributes: {
 +   birthdate: {
 +     required: false,
-+     immutable: true,
++     mutable: false,
 +   },
 + },
 });
@@ -266,7 +266,7 @@ async function handleSignUpConfirmation({ username, confirmationCode }) {
 The `autoSignIn` API will automatically sign-in a user when it was previously enabled by the `signUp` API and after any of the following cases has completed:
 
 - User confirmed their account with a verification code sent to their phone or email (default option).
-- User confirmed their account with a verification link sent to their phone or email. In order to enable this option you need to go to the [Amazon Cognito console](https://aws.amazon.com/pm/cognito), look for your userpool, then go to the `Messaging` tab and enable `link` mode inside the `Verification message` option. Finally you need to define the `signUpVerificationMethod` to `link` inside the `Cognito` option of your `Auth` config.
+- User confirmed their account with a verification link sent to their phone or email. In order to enable this option you need to set `loginWith.email.verificationEmailStyle` to `LINK` in your auth resource file (`amplify/auth/resource.ts`)
 
 ```ts
 import { autoSignIn } from 'aws-amplify/auth';