Cherry-pick #21745 to 7.x: Agent atomic installer

[michalpristas]

Cherry-pick of PR #21745 to 7.x branch. Original message:

Cherry-pick also dependencies: #21735 and #21706

What does this PR do?

This PR makes unpacking an "atomic" operation by unpacking to temporary location and then moving it to the correct place, this should solve some rare issues which manifests when agent got killed during installation of beats and results in half-unpacked archive to be understood as correct installation

I tested this change on darwin/linux/windows and using local e2e test suite.

Fixes: #21718

Why is it important?

Makes agent more reliable

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

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Pinging @elastic/ingest-management (Team:Ingest Management)

[elasticmachine]

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Build stats

• Build Cause: [Pull request #21779 updated]

• Start Time: 2020-10-14T06:59:02.672+0000

• Duration: 39 min 15 sec

Test stats 🧪

Test	Results
Failed	0
Passed	1394
Skipped	4
Total	1398

[blakerouse]

Backport looks good.