Lambda@Edge origin response event errors out with 502 error because read-only header was deleted

The Cloudfront request responds with:
```The Lambda function result failed validation: The function tried to add, delete, or change a read-only header. We can't connect to the server for this app or website at this time. There might be too much traffic or a configuration error. Try again later, or contact the app or website owner.```

From CloudWatch logs:
```ERROR Validation error: Lambda function result failed validation, the function tried to delete read-only header, headerName : Transfer-Encoding.```

I've figured out a workaround that is to just copy the header manually, but I wonder if the library should've taken care of that itself?

```js
import { getCurrentInvoke } from '@vendia/serverless-express';

router.get('/*', (req, res) => {
const { event } = getCurrentInvoke();

if (event.Records[0].cf.response.headers['transfer-encoding']) {
res.setHeader(
'Transfer-Encoding',
event.Records[0].cf.response.headers['transfer-encoding'][0].value,
);
}
```

Verfolge den Lambda@Edge-Origin-Response-Pfad und die Verarbeitung der Response-Header rund um getCurrentInvoke(), mit Fokus auf den Transfer-Encoding-Header, der im CloudWatch-Validierungsfehler angezeigt wird. Reproduziere die CloudFront-502-Response und überprüfe, dass die resultierende Response nicht mehr versucht, einen schreibgeschützten Header zu löschen.

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