[8.x](backport #40707) Update fields to use mapstr in vSphere virtualmachine metricset

[mergify]

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.

---

This is an automatic backport of pull request #40707 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of e7637c0 has failed:

On branch mergify/bp/8.x/pr-40707
Your branch is up to date with 'origin/8.x'.

You are currently cherry-picking commit e7637c08b2.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   CHANGELOG.next.asciidoc
	modified:   metricbeat/docs/fields.asciidoc
	modified:   metricbeat/module/vsphere/virtualmachine/_meta/fields.yml
	modified:   metricbeat/module/vsphere/virtualmachine/virtualmachine_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   metricbeat/module/vsphere/fields.go
	both modified:   metricbeat/module/vsphere/virtualmachine/_meta/data.json
	both modified:   metricbeat/module/vsphere/virtualmachine/data.go
	both modified:   metricbeat/module/vsphere/virtualmachine/data_test.go
	both modified:   metricbeat/module/vsphere/virtualmachine/virtualmachine.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[botelastic]

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

[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 mergify/bp/8.x/pr-40707 upstream/mergify/bp/8.x/pr-40707
git merge upstream/8.x
git push upstream mergify/bp/8.x/pr-40707

[mergify]

This pull request has not been merged yet. Could you please review and merge it @ishleenk17? 🙏

[mergify]

This pull request has not been merged yet. Could you please review and merge it @ishleenk17? 🙏

[mergify]

This pull request has not been merged yet. Could you please review and merge it @ishleenk17? 🙏

[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 mergify/bp/8.x/pr-40707 upstream/mergify/bp/8.x/pr-40707
git merge upstream/8.x
git push upstream mergify/bp/8.x/pr-40707

[ishleenk17]

Ignoring lint errors as they were not present in the actual PR.