[Onboarding] Update the Quickstart doc for monitoring of Hosts.

The 'Quickstart: Monitor hosts with Elastic Agent' doc should be updated.

This functionality is available as GA in 8.16.
This functionality is available in all Elastic deployment models.
This functionality can auto-detect 14 Integrations in 81.6.
Under 'Collect your data' the screenshot in step 3 needs to be updated.
Under 'need to scan your host again', we should specify the name of the auto-detect script as well as the folder in which it can be found.
The 'Visualise your data' section needs to be updated to include the additional Integrations that can now be supported OOTB.

Please reach out to @thomheymann or @akhileshpok for clarifications on any of the above items.

elastic / observability-docs