[ML] Transforms: Reduces rerenders and multiple fetches of source index on transform wizard load.

[walterra]

Summary

Adds checks to avoid unnecessary initial rerenders and refetches of data when loading the transform wizard. This reduces rerenders from 14 to 11 and more importantly the request to fetch index data is triggered only once instead of three times. One of the requests even triggered an error which could briefly trigger a callout on slower connections.

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)

[qn895]

Changes LGTM 🎉

[darnautov]

Code LGTM

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: b2f27f3

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	404.5KB	404.6KB	+68.0B

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	14	16	+2
securitySolution	408	412	+4
total			+6

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	15	17	+2
securitySolution	487	491	+4
total			+6

History

• 💚 Build #139388 succeeded 39805de

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@elasticmachine merge upstream

cc @walterra