[ML] Transforms: Use estypes.TransformGetTransformStatsTransformStats for transform stats.

[walterra]

Summary

Gets rid of a lot of the manually defined attributes of TransformStats by extending from estypes.TransformGetTransformStatsTransformStats.

How we treat the transform health status needed to be adapted because the types provided by estypes are both lower and upper case (e.g. green/GREEN) but lack the unknown status we use in the UI. mapEsHealthStatus2TransformHealthStatus() is used to transform a health status returned via API to the one we use in the UI.

Checklist

• Unit or functional tests were updated or added to match the most common scenarios
• This was checked for breaking API changes and was labeled appropriately

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[darnautov]

LGTM

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 1c3d38f

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
transform	391.9KB	392.1KB	+192.0B

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
transform	18.5KB	18.7KB	+163.0B

History

• 💚 Build #202396 succeeded 2711c56
• 💔 Build #202262 failed d916ac9
• 💔 Build #202175 failed 0235718
• 💔 Build #202123 failed 31fa4cc
• 💔 Build #202093 failed 55ec826
• 💔 Build #202048 failed 21cb5f8

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

cc @walterra

[qn895]

Code LGTM 🎉