[7.16](backport #27355) [Metricbeat] Add Linux pressure metricset

[mergify]

This is an automatic backport of pull request #27355 done by Mergify.
Cherry-pick of e49f257 has failed:

On branch mergify/bp/7.16/pr-27355
Your branch is up to date with 'origin/7.16'.

You are currently cherry-picking commit e49f2579c2.
  (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/docs/modules/linux.asciidoc
	new file:   metricbeat/docs/modules/linux/pressure.asciidoc
	modified:   metricbeat/include/list_common.go
	modified:   metricbeat/metricbeat.reference.yml
	modified:   metricbeat/module/linux/_meta/config.yml
	new file:   metricbeat/module/linux/pressure/_meta/data.json
	new file:   metricbeat/module/linux/pressure/_meta/docs.asciidoc
	new file:   metricbeat/module/linux/pressure/_meta/fields.yml
	new file:   metricbeat/module/linux/pressure/_meta/testdata/proc/pressure/cpu
	new file:   metricbeat/module/linux/pressure/_meta/testdata/proc/pressure/io
	new file:   metricbeat/module/linux/pressure/_meta/testdata/proc/pressure/memory
	new file:   metricbeat/module/linux/pressure/pressure_test.go
	modified:   metricbeat/modules.d/linux.yml.disabled
	modified:   x-pack/metricbeat/metricbeat.reference.yml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   metricbeat/docs/modules_list.asciidoc
	both modified:   metricbeat/module/linux/fields.go
	both added:      metricbeat/module/linux/pressure/pressure.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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[elasticmachine]

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• Start Time: 2021-11-19T00:51:34.714+0000

• Duration: 89 min 27 sec

• Commit: a1efd40

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Test	Results
Failed	0
Passed	9310
Skipped	2344
Total	11654

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[b-deam]

@fearful-symmetry - am I good to squash & merge here?