[Heartbeat] Include packet stats in ICMP checks

[awahab07]

Describe the enhancement:

For ICMP checks, Heartbeat only reports the number of requests sent and rtt metric e.g. the following info is included in ICMP summary documents:

{
  "icmp": {
    "requests": 1,
    "rtt": {
      "us": 115664
    }
  }
}

Heartbeat should include the packet information as well in the summary document, e.g.:

{
  "icmp": {
    "requests": 1,
    "rtt": {
      "us": 115664
    },
    "packets": {
      "transmitted": 10,
      "received": 5,
      "loss": 0.5
    }
  }
}

Describe a specific use case for the enhancement or feature:

Competitor observability solutions provide packet stats to measure the performance of a network along with the health of a network or reachability to a host. With Heartbeat's current ICMP output, host reachability can be measured but host's network health cannot be measured.

The enhanced output will be utilized to create Network Performance kind of dashboards and packet stats can be displayed on Synthetics UI for ICMP monitors. It'll also allow the customers migrating to Elastic from other vendors to retain the same depth of information they have been using.

[elasticmachine]

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

[vigneshshanmugam]

Linking the original thread from community for awareness - https://elasticstack.slack.com/archives/C05AJM4F7PU/p1704322731698519