[exporter/elasticsearch] Support preserving attributes when mapping to ECS

[ChrsMark]

Description:

This PR adds support for preserving resource attributes that are valid ECS fields in addition of mapping them. At the moment the host.name is mapped to the host.hostname. Both are valid ECS fields but can differ in some cases. Since there is no such distinction in SemConv right now, it does makes sense to preserve both.

refs:

• https://www.elastic.co/guide/en/ecs/current/ecs-host.html#field-host-name
• https://www.elastic.co/guide/en/ecs/current/ecs-host.html#field-host-hostname

Link to tracking Issue:

Testing:

Using the testing notes from #33622.

Stored document:

 {
    "app": {
      "label": {
        "component": "migration-logger"
      }
    },
    "kubernetes": {
      "node": {
        "name": "kind-control-plane"
      },
      "pod": {
        "uid": "0eda57cd-a4ae-4e89-88fa-c771d3bf0c77",
        "name": "daemonset-logs-4sqjq"
      },
      "namespace": "default"
    },
    "agent": {
      "name": "otlp"
    },
    "@timestamp": "2024-06-20T07:27:42.589678923Z",
    "log": {
      "iostream": "stdout",
      "file": {
        "path": "/var/log/pods/default_daemonset-logs-4sqjq_0eda57cd-a4ae-4e89-88fa-c771d3bf0c77/busybox/0.log"
      }
    },
    "service": {
      "name": "migration-logger"
    },
    "k8s": {
      "container": {
        "restart_count": "0",
        "name": "busybox"
      },
      "pod": {
        "start_time": "2024-06-20T07:27:21Z"
      },
      "daemonset": {
        "name": "daemonset-logs"
      }
    },
    "host": {
      "hostname": "daemonset-opentelemetry-collector-agent-l6pzp",
      "os": {
        "type": "linux",
        "platform": "linux"
      },
      "name": "daemonset-opentelemetry-collector-agent-l6pzp"
    },
    "time": "2024-06-20T07:27:42.589678923Z",
    "message": "otel logs at 07:27:42",
    "logtag": "F"
  }

Documentation: ~

/cc @lahsivjar @andrzej-stencel @carsonip

[gregkalapos]

More context on the history of these two fields can be seen in elastic/ecs#144 (comment).

Since there is no such distinction in SemConv right now, it does makes sense to preserve both.

➕ on this.
SemConv says: "...On Unix ... contain what hostname ... returns, or the fully qualified hostname, or another name specified by the user." -> In ECS user specified would be host.name, otherwise either host.name or host.hostname. But we don't know from OTel data if it's user specified or not, so I agree, best is to populate both.

[lahsivjar]

LGTM (one comment on the changelog).