Cherry-pick #22987 to 7.x: Align logging with ECS

[michalpristas]

Cherry-pick of PR #22987 to 7.x branch. Original message:

What does this PR do?

This PR enables ECS loggin back so log.level is reported correctly.
On top of that it drops ecs.version as ecs.version is already added by libbeat (to deal with #21616)

Without drop events contains two ecs version fields one composed another one not e.g

"ecs.version": "1.6.0",
"ecs": {
  "version": "1.6.0",
}

Why is it important?

Fixes: #22858

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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• Build Cause: Pull request #23015 opened

• Start Time: 2020-12-09T07:35:17.198+0000

• Duration: 32 min 46 sec

Test stats 🧪

Test	Results
Failed	0
Passed	1384
Skipped	6
Total	1390

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Test stats 🧪

Test	Results
Failed	0
Passed	1384
Skipped	6
Total	1390

[blakerouse]

Backport looks good.