[Upgrade Assistant] Fix small issue with unknown indicators

[sabarasaba]

Closes #186247

Summary

The ES api can sometimes return an indicator that has status unknown and that only has a symptom (no details). For example: disk: { status: 'unknown', symptom: 'No disk usage data.' }. This PR makes sure that the UI doesnt break in this specific scenario and creates a warning indicator anyway with the minimal information that was provided by the API.

How to test

• Start up kibana and es
• Run the following command in console:

 PUT _cluster/settings
 {
     "persistent": {
         "health.node.enabled": false
     }
 }

• Navigate to Stack management -> Upgrade assistant
• Verify that:
  • ES deprecations box shows one warning
  • Clicking on it goes to the es_deprecations page and a No disk usage deprecation is shown.

[sabarasaba]

/ci

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 6fa0e54

Failed CI Steps

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
upgradeAssistant	157.0KB	157.0KB	+3.0B

History

• 💔 Build #218988 failed e4092d8

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @sabarasaba

[elasticmachine]

Pinging @elastic/kibana-management (Team:Kibana Management)

[ElenaStoeva]

Thanks for working on this @sabarasaba! Tested locally and the UI works now.
I left a comment regarding future-proofing against similar scenarios with no details field provided. Let me know what you think.

[sabarasaba]

@elasticmachine merge upstream

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 5c200ad

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
upgradeAssistant	157.0KB	157.0KB	+3.0B

cc @sabarasaba