[7.x](backport #28452) [Heartbeat] Update step name field to use keyword and text

[mergify]

This is an automatic backport of pull request #28452 done by Mergify.
Cherry-pick of 539edc8 has failed:

On branch mergify/bp/7.x/pr-28452
Your branch is up to date with 'origin/7.x'.

You are currently cherry-picking commit 539edc8385.
  (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:   heartbeat/_meta/fields.common.yml
	modified:   heartbeat/docs/fields.asciidoc

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   heartbeat/include/fields.go
	both modified:   x-pack/heartbeat/include/fields.go

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

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• Start Time: 2021-10-18T16:54:36.562+0000

• Duration: 78 min 47 sec

• Commit: 858d305

Test stats 🧪

Test	Results
Failed	0
Passed	3553
Skipped	80
Total	3633

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