Sample JSON:

```
{
  "method": "GET",
  "path": "/admin",
  "format": "html",
  "controller": "Admin::DashboardController",
  "action": "index",
  "status": 500,
  "duration": 2584.11,
  "view": 0,
  "db": 9.21,
  "time": "2019-11-14T13:12:46.156Z",
  "params": [],
  "remote_ip": "127.0.0.1",
  "user_id": 1,
  "username": "root",
  "ua": "Mozilla/5.0",
  "queue_duration": 274.35,
  "correlation_id": "KjDVUhNvvV3",
  "cpu_s": 2.837645135999999,
  "exception": {
    "class": "NameError",
    "message": "undefined local variable or method `adsf'",
    "backtrace": [
      "app/controllers/admin/dashboard_controller.rb:11:in `index'",
      ...
    ]
  }
}
```

This change also drops the `error` field in favor of `exception.class`
and `exception.message`.

Closes https://gitlab.com/gitlab-org/gitlab/issues/36297