[DOCS]: Host List Overview about security-docs

[kevinlog]

@jmikell821
Currently, the Endpoint will reflect whichever status the parent Agent has, so these are from an Agent perspective. It still gives Security users insight into their Endpoint in the Administration tab

Possible Host statuses:

• Online, Green. This indicates that the Agent is online and communicating with Kibana
• Unenrolling, Yellow. This indicates that the Agent is currently unenrolling and will soon be removed from Ingest and the Endpoint will follow.
• Grey, Offline. This indicates that the Agent is still enrolled, but may be on a machine that is shutdown or doesn't have internet access currently. In this state, the Agent is no longer communicating with Kibana on a regular interval
• Red, Error. This indicates an Error in the Agent and means something has gone wrong. The user should look at the Agent logs in Fleet to find out more. This can also mean that the Endpoint is unable to find the parent Agent or that is it missing the Agent ID. This is also a problem and the user should investigate Endpoint or Agent logs.

FYI @caitlinbetz