Apple OAuth2 example doesn't work

### Prerequisites

- [X] I have written a descriptive issue title
- [X] I have searched existing issues to ensure the bug has not already been reported

### Fastify version

4.26.1

### Plugin version

7.8.0

### Node.js version

v20.6.1

### Operating system

Windows

### Operating system version (i.e. 20.04, 11.3, 10)

10

### Description

I created the issue, so that it clarifies the issue or helps other people.

I had to make changes to make the example work. `examples/apple.js`

Explicitly setting scope to empty (otherwise undefined error) `scope: [], //'name', 'email'` , when I set scope apple returns POST form-urlencoded. That is documented in the example and Github issues. It might be nice to provide an example for that case as well.

`const { code, state, error, user } = request.query` instead of `request.body`

Wher does `Error.CancelledAuth` comes from? It is undefined so it has wrong logic when error is also undefined.

The part I didn't understand:
`request.cookies['oauth2-redirect-state']` this is empty, however the cookie is set in browser dev tools.

Readme states, "Since v7.2.0, @fastify/oauth2 requires the use of cookies to securely implement the OAuth2 exchange." It is after this example is updated on the repo.

### Steps to Reproduce

Create a new project `npm init fastify` and try `examples/apple.js` example

### Expected Behavior

_No response_