Describe the enhancement:

When configuring metrics inputs in Elastic Agent, user should be able to pass Metricbeats --system.hostfs equivalent.

Describe a specific use case for the enhancement or feature:

I'd like to monitor a host out of a container that's running on it. With raw Metricbeat I can mount the hosts /proc directory in the container and pass it with the --system.hostfs flag on the command line. I don't think that's currently possible with Elastic Agent.

To improve past what Metricbeat offers, this could be part of the config instead of command line flag.