[Heartbeat/Synthetics] Network Discovery Functionality

[Erikg346]

Describe the enhancement:
I would like Heartbeat can be able to scan a network, determine hosts/ip, and report back hosts' ICMP status, up and down.
Think NMAP but built-in. It can be run on specified intervals just like how we currently create monitors. The current way we can "scan" is by manually inputting ICMP monitors. This has become a hassle and super tedious.

Describe a specific use case for the enhancement or feature:
Our team has used other competitor's monitoring tools and they offer network discovery. It's an important thing for being able to quickly determine if a host is pingable or not.

[elasticmachine]

Pinging @elastic/obs-ds-hosted-services (Team:obs-ds-hosted-services)

[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!