[Docs]: Incorrect link for Quick Start guide for ExtAuth

### I confirm that: - [x] This issue is about the **documentation website**, NOT about the Navidrome server ### Page URL or path https://www.navidrome.org/docs/usage/integration/authentication/ ### What's wrong Link to Quick Start guide at top of page is a 404. **Link is:** /docs/usage/configuration/extauth-quickstart/ ### Suggested fix **Link should be:** /docs/getting-started/extauth-quickstart/