Add logging.ecs parameter

[simitt]

Motivation/summary

* Update beats to a9be1b56a849

• Add logging.ecs parameter to config files

Forwardport of #3749

Checklist

- [ ] I have signed the Contributor License Agreement.

• I have updated CHANGELOG.asciidoc

I have considered changes for:

• documentation
  -> already updated
• logging (add log lines, choose appropriate log selector, etc.)
  -> follow up beater/middleware: update fields to be ECS-compliant #3796
• automated tests (add tests for the code changes, all unit tests pass locally)
  -> tested in libbeat

How to test these changes

see #3749

Related issues

#3155

[apmmachine]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request #3815 updated]

• Start Time: 2020-05-25T15:27:24.363+0000

• Duration: 47 min 8 sec

Test stats 🧪

Test	Results
Failed	0
Passed	3227
Skipped	145
Total	3372

Steps errors

Expand to view the steps failures

• Name: Test Sync

  • Description: ./script/jenkins/sync.sh

  • Duration: 3 min 49 sec

  • Start Time: 2020-05-25T15:37:59.457+0000

  • log

[codecov-commenter]

Codecov Report

Merging #3815 into master will increase coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3815      +/-   ##
==========================================
+ Coverage   79.81%   79.89%   +0.08%     
==========================================
  Files         136      136              
  Lines        6158     6158              
==========================================
+ Hits         4915     4920       +5     
+ Misses       1243     1238       -5     

Impacted Files	Coverage Δ
kibana/connecting_client.go	72.58% <0.00%> (+8.06%)	⬆️

[simitt]

I removed the beats update from this PR as the required part for the ECS logging was already in master, and the update would have contained unrelated agent.hostname changes.