Add daemonset datastream for k8s package & system tests

[ChrsMark]

What does this PR do?

This PR:

1. adds daemonset datastream introduced by Kubernetes state_daemonset metricset for Metricbeat beats#20649 as part of Migrate Kubernetes integration #511, based on migration assessment
2. Adds system tests for the datastreams using mock k8s APIs

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all datasets collect metrics or logs.

[elasticmachine]

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Build stats

• Build Cause: Pull request #569 updated

• • Start Time: 2021-02-02T08:10:44.140+0000

• Duration: 29 min 28 sec

• Commit: f0b7841

Test stats 🧪

Test	Results
Failed	0
Passed	87
Skipped	0
Total	87

[ChrsMark]

@mtojek it could be merged as is but not sure if we should merge yet. However, I would like your eyes on this at this stage.

[mtojek]

LGTM. I think we can merge it and even push it to snapshot. We don't need to promote it further.

[ChrsMark]

OK merging this one for now, thanks for reviewing!

[ChrsMark]

Ah, CI failed. Checking...

[mtojek]

Hm.. it looks like it passed.