Cherry-pick #17894 to 7.x: Agent push ECS meta to fleet

[michalpristas]

Cherry-pick of PR #17894 to 7.x branch. Original message:

What does this PR do?

This PR enhances local metadata sent to fleet on checkin and enroll to conform to ecs format.
It still keeps 3 items it was sending before which will be removed when kibana confirms it does not need it.

Why is it important?

Fixes: #14461

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 (Project:fleet)

[ph]

@michalpristas as @ruflin noted in the sync this will indeed be a problem we need to send an object to Kibana. I have updated the issues in elastic/kibana#64173 to mention its an object. I believe we have a method in common package that can exploded the keys into multiples nested object.. I haven't found it.

[ph]

@michalpristas Can you sync with @nchaulet so we have the appropriate change at the same time?

[michalpristas]

@nchaulet ping me when you have a PR ready i will do the change overnight and test it with your branch. we can merge at the same day so snapshots are ok

[elasticmachine]

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• Build Cause: [Pull request Cherry-pick #17894 to 7.x: Agent push ECS meta to fleet  #17921 updated]

• Start Time: 2020-05-04T15:32:35.042+0000

• Duration: 40 min 37 sec (2377285)

• Commit: 04f6073