Add config parsing for disable_host to FunctionBeat

[msluther]

Describe the enhancement:

This PR was merged May 2020:
#18159

That means there is now logic in libbeats to be able to skip adding host: { name } into the output. The option to configure this should get pulled into functionbeat as well as filebeat (perhaps other beats as well?)

Describe a specific use case for the enhancement or feature:

FunctionBeats run as a serverless function. In AWS this means a Lambda that runs and processes some input pipe of events. The host that gets written by functionbeat ends up being the host running the serverless function and not the host that wrote the source event. Having the ability to skip this incorrect data being written into our system is fairly imperative. It also makes it easier to find any events being created that aren't conforming to ECS and are missing host.name so that those events could be fixed.

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[botelastic]

Hi!
We just realized that we haven't looked into this issue in a while. We're sorry!

We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1.
Thank you for your contribution!

[msluther]

👍

[botelastic]

Hi!
We just realized that we haven't looked into this issue in a while. We're sorry!

We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1.
Thank you for your contribution!