Add orchestrator cluster ECS fields in k8s events

[ChrsMark]

What does this PR do?

This PR adds ECS orchestrator fields for k8s events. This is not happening at the moment because events are being collected through "watchers" and the metadata generators are not applicable due to the nature of these objects. However we can directly add orchestrator metadata about the cluster.

Why is it important?

In order to be able to filter out events per cluster on Dashboards.

Closes elastic/integrations#3114

Sample ES event:

{
  "@timestamp": "2022-04-19T08:40:34.347Z",
  "@metadata": {
    "beat": "metricbeat",
    "type": "_doc",
    "version": "8.3.0"
  },
  "ecs": {
    "version": "8.0.0"
  },
  "host": {
    "name": "kind-control-plane"
  },
  "agent": {
    "type": "metricbeat",
    "version": "8.3.0",
    "ephemeral_id": "118c830a-fc6a-46f2-b99a-b7cd29d53350",
    "id": "b210221a-9944-4f3d-8920-6fa617f66a24",
    "name": "kind-control-plane"
  },
  "kubernetes": {
    "event": {
      "reason": "Pulling",
      "type": "Normal",
      "count": 1,
      "source": {
        "component": "kubelet",
        "host": "kind-control-plane"
      },
      "involved_object": {
        "uid": "46c9d822-5415-49e5-8c1f-cfcb8e110ec2",
        "api_version": "v1",
        "resource_version": "353488",
        "name": "busybox",
        "kind": "Pod"
      },
      "metadata": {
        "resource_version": "353495",
        "timestamp": {
          "created": "2022-04-19T08:40:34.000Z"
        },
        "name": "busybox.16e73f86433fba9c",
        "namespace": "default",
        "self_link": "",
        "generate_name": "",
        "uid": "ea38e90c-c262-4e74-ac72-af6b6844605f"
      },
      "timestamp": {
        "first_occurrence": "2022-04-19T08:40:34.000Z",
        "last_occurrence": "2022-04-19T08:40:34.000Z"
      },
      "message": "Pulling image \"busybox:1.28\""
    }
  },
  "orchestrator": {
    "cluster": {
      "url": "kind-control-plane:6443",
      "name": "kind"
    }
  },
  "metricset": {
    "name": "event"
  },
  "event": {
    "dataset": "kubernetes.event",
    "module": "kubernetes"
  },
  "service": {
    "type": "kubernetes"
  }
}

[botelastic]

This pull request doesn't have a Team:<team> label.

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2022-04-19T10:27:52.556+0000

• Duration: 52 min 48 sec

Test stats 🧪

Test	Results
Failed	0
Passed	3533
Skipped	877
Total	4410

💚 Flaky test report

Tests succeeded.

🤖 GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

• /package : Generate the packages and run the E2E tests.

• /beats-tester : Run the installation tests with beats-tester.

• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)

[tetianakravchenko]

LGTM

[MichaelKatsoulis]

LGTM