Heartbeat Autodiscover documentation uses `hosts` instead of `urls` for HTTP

Hi,

In the Autodiscover documentation page of Heartbeat, the example for Kubernetes uses hosts under the HTTP configuration, whereas it should be urls. I spent an hour or so digging into this.

https://www.elastic.co/guide/en/beats/heartbeat/current/configuration-autodiscover.html

If you set hosts instead of urls, following the example, you get:

Check failed for config &{{<nil> } <nil> 0xc42011fd40}: job err missing required field accessing 'urls', won't start runner

Thank you for pointing this out.
issue opened