Class UnauthorizedError public

A UnauthorizedError equates to a HTTP 401 Unauthorized response status. It is used by an adapter to signal that a request to the external API was rejected because authorization is required and has failed or has not yet been provided.

An example use case would be to redirect the user to a login route if a request is unauthorized:

```js {data-filename=app/routes/application.js} import Route from '@ember/routing/route'; import { UnauthorizedError } from '@ember-data/adapter/error'; import { action } from '@ember/object';

export default class ApplicationRoute extends Route {