[7.17](backport #31001) Filesystem refactor

[mergify]

This is an automatic backport of pull request #31001 done by Mergify.
Cherry-pick of 1d4a7ca has failed:

On branch mergify/bp/7.17/pr-31001
Your branch is up to date with 'origin/7.17'.

You are currently cherry-picking commit 1d4a7ca00e.
  (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/system/filesystem/_meta/docs.asciidoc
	deleted:    metricbeat/module/system/filesystem/helper_test.go
	modified:   metricbeat/module/system/fsstat/_meta/data.json

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   go.sum
	both modified:   metricbeat/module/system/fields.go
	both modified:   metricbeat/module/system/filesystem/_meta/fields.yml
	both modified:   metricbeat/module/system/filesystem/filesystem.go
	both modified:   metricbeat/module/system/filesystem/filesystem_test.go
	deleted by them: metricbeat/module/system/filesystem/helper.go
	both modified:   metricbeat/module/system/fsstat/fsstat.go
	both modified:   metricbeat/module/system/test_system.py

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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[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[elasticmachine]

💔 Build Failed

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Build stats

• Start Time: 2022-09-15T23:34:20.074+0000

• Duration: 209 min 15 sec

Test stats 🧪

Test	Results
Failed	0
Passed	21614
Skipped	1436
Total	23050

Steps errors

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Building Beats » Beats Packaging » PR-33022

• Took 116 min 16 sec . View more details here
• Description: null

💚 Flaky test report

Tests succeeded.

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[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/7.17/pr-31001 upstream/mergify/bp/7.17/pr-31001
git merge upstream/7.17
git push upstream mergify/bp/7.17/pr-31001

[mergify]

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

[fearful-symmetry]

Tests are still failing, not quite sure why.

[fearful-symmetry]

Alright, tested this manually. If there's still dependency issues I'm just gonna merge this

[mergify]

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