[Ingest Manager] Align logging with ECS

[michalpristas]

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.

[elasticmachine]

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

[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: Pull request #22987 opened

• Start Time: 2020-12-08T14:28:59.855+0000

• Duration: 24 min 15 sec

Test stats 🧪

Test	Results
Failed	0
Passed	1396
Skipped	4
Total	1400

💚 Flaky test report

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Test stats 🧪

Test	Results
Failed	0
Passed	1396
Skipped	4
Total	1400

[blakerouse]

Looks good.