Add swap to memory fields

[fearful-symmetry]

What does this PR do?

This is a fix for #3120. Just adding a few fields to the one memory datastream.

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.
• I have verified that Kibana version constraints are current according to guidelines.

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

[elasticmachine]

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Build stats

• Start Time: 2022-05-10T15:33:00.735+0000

• Duration: 23 min 41 sec

Test stats 🧪

Test	Results
Failed	0
Passed	25
Skipped	0
Total	25

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (0/0)	💚
Files	100.0% (0/0)	💚 3.589
Classes	100.0% (0/0)	💚 3.589
Methods	51.515% (17/33)	👎 -36.769
Lines	100.0% (0/0)	💚 10.972
Conditionals	100.0% (0/0)	💚