Add _meta information to Kubernetes fields

[ChrsMark]

What does this PR do?

This change updates fields.yml defintions to include units and metric type information so as to enhance meta information for each collected Kubernetes fields in accordance with elastic/elasticsearch#61941. More example here.

Related issues

• Closes Add _meta information to Kubernetes fields #934

[elasticmachine]

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Build stats

• Build Cause: Pull request #1289 updated

• Start Time: 2021-07-06T08:01:55.859+0000

• Duration: 28 min 13 sec

• Commit: 0a133ff

Test stats 🧪

Test	Results
Failed	0
Passed	109
Skipped	0
Total	109

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[mtojek]

LGTM