update fields to include new cgroupsV2 fields

[fearful-symmetry]

What does this PR do?

This updates the integration with the fields changes that are already in Beats, namely cgroups V2 support.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.

How to test this PR locally

• Pull down and build
• Run on a system running cgroups V2 (Like the latest fedora release)
• Make sure system/process collects all the data it should, and that all fields are documented.

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[elasticmachine]

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Build stats

• Start Time: 2021-08-17T21:49:14.665+0000

• Duration: 16 min 27 sec

• Commit: 2596835

Test stats 🧪

Test	Results
Failed	0
Passed	266
Skipped	0
Total	266

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