add clarity on how to handle confirmSignIn() and signIn() API responses for nextStep property

**Describe the content issue**:
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We need to update the `confirmSignIn()` documentation to better clarify how to handle when this API returns `CONFIRM_SIGN_IN_WITH_NEW_PASSWORD_REQUIRED` as the `nextStep`. This is described in detail within the `amplify-js` issue [#13598](https://github.com/aws-amplify/amplify-js/issues/13598).

**URL page where content issue is**:
https://docs.amplify.aws/react/build-a-backend/auth/connect-your-frontend/sign-in/#using-the-signin-api