Propagate checkin status to agent record

[scunningham]

What does this PR do?

Writes out the checkin status field to the last_checkin_status field in the agent record. This is necessary to support UX changes.

Why is it important?

UX needs it.

Checklist

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

How to test this PR locally

Setup local fleet server and point an agent at it. You can validate field change using the dev tools in kibana.

Screenshots

[elasticmachine]

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Build stats

• Build Cause: Pull request #420 updated

• Start Time: 2021-06-02T20:56:41.053+0000

• Duration: 4 min 19 sec

• Commit: a97f374

Test stats 🧪

Test	Results
Failed	0
Passed	178
Skipped	0
Total	178

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[jen-huang]

@ph / @urso This seems like a good candidate to backport to 7.13, what do you think?

[scunningham]

I wouldn't backport unless we were backporting the new UX as well. Not sure we are buying ourselves much otherwise.

[jen-huang]

@scunningham We already have code in Fleet that looks at last_checkin_status from pre-Fleet Server days, not just for new UX, so this seems like a regression with agent status reporting that we didn't catch in testing.

[jfsiii]

🚀 Thanks for getting this in so quickly. I ran this branch locally and, without any Kibana changes, it now shows an Unhealthy badge for an agent with last_checkin_status of degraded.

Without these changes, the UI marks the agents as Healthy

[ph]

@scunningham based on the discussion from @jen-huang and the comment from @jfsiii I would backport this to 7.13.x too. If it's fine with you I will just add the label.

[scunningham]

@ph I have no objection.