Include sign in with apple variables in the default supported environment variables

**Is your feature request related to a problem?
Recently sign in with apple option is added to the supported options in the CLI (5.1.2). However, the console environment variables page does not specify the default variables for sign in with apple . Please update it.

[https://docs.aws.amazon.com/amplify/latest/userguide/environment-variables.html](https://docs.aws.amazon.com/amplify/latest/userguide/environment-variables.html)

**Describe the solution you'd like**
Some thing like this


Start with the linked AWS Amplify environment-variables page and compare its default supported variables with the Sign in with Apple support added in CLI 5.1.2. Update the page so the relevant default variables are listed, and consider the work done when the documentation matches the requested variables.

Written by the indexing model from the issue text.