Following REST tutorial results in error

**Describe the content issue**:
Running the application after following the tutorial results in an error.

```
[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: ConfigurationError {
"message": "No Cognito plugin config available"
}
```

amplify-cli version: 12.7.1

**URL page where content issue is**:

https://docs.amplify.aws/lib/restapi/getting-started/q/platform/flutter/

Start with the Flutter REST API tutorial at the linked documentation URL and reproduce the error using amplify-cli 12.7.1. Check the tutorial's setup and configuration steps against the reported missing Cognito plugin config; done means the tutorial can be followed without this runtime error.

Written by the indexing model from the issue text.