[GCP] Region and zone ecs fields nested in cloud field

[ishleenk17]

The regsion and zone ecs fields were present as below:

{
  "cloud": {
    "account": {
      "id": "acount-id-1",
      "name": "account-name-1"
    },
    "instance": {
      "id": "111111",
      "name": "test-name"
    },
    "machine": {
      "type": "f1-micro"
    },
    "provider": "gcp"
  },
  "cloud.availability_zone": "asia-northeast1-a",
  "cloud.region": "asia-northeast1"
  ...

These fields have now been nested and event will look like this after thae change:

{
  "cloud": {
    "account": {
      "id": "acount-id-1",
      "name": "account-name-1"
    },
    "instance": {
      "id": "111111",
      "name": "test-name"
    },
    "machine": {
      "type": "f1-micro"
    },
    "provider": "gcp",
    "availability_zone": "asia-northeast1",
    "region": "asia-northeast1"
  },
  ...

}

Proposed commit message

See title

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Related issues

• Closes [MetricBeat][GCP] ecs field cloud.region, cloud.availability_zone should be nested in cloud field #35098

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b gcp_nested upstream/gcp_nested
git merge upstream/main
git push upstream gcp_nested

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @ishleenk17? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[elasticmachine]

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• Start Time: 2023-11-02T05:15:29.399+0000

• Duration: 57 min 43 sec

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[zmoog]

LGTM!