[ML] Adds anomaly description as an alert message for anomaly detection rule type

[darnautov]

Summary

Closes #136391

Uses a description of the anomaly for the alert message for anomaly detection alerting rules with the record result type. This messages is used for example in the Reason field in the alert table and details flyout.

Checklist

• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[peteharverson]

Tested latest changes and LGTM.

Just left a suggestion for the i18n props.

[darnautov]

@elasticmachine merge upstream

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: e23e817

Failed CI Steps

• FTR Configs #33

Test Failures

• [job] [logs] FTR Configs #33 / Uptime app with real-world data overview page pagination is cleared when filter criteria changes

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
ml	1867	1868	+1

Async chunks

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

id	before	after	diff
ml	3.6MB	3.6MB	+69.0B

History

• 💔 Build #181901 failed 62dd466
• 💛 Build #181333 was flaky e3c644b

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

cc @darnautov