Update documentation about KatibConfig API

[tenzen-y]

/kind feature

Describe the solution you'd like
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Because we improve the KatibConfig In #2176, we need to update the docs about katib-config.

https://www.kubeflow.org/docs/components/katib/katib-config/

Also, updating the Debveloper Guide because we introduced Golang better way to the Katib since #2176.

• Using go-cmp instead of reflect would be more useful in the test since avoiding eyeball grep 👀
• Defining test cases as maps instead of slices would be more reasonable since we can avoid depending on the running order.

Anything else you would like to add:
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[tenzen-y]

/assign

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This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[tenzen-y]

/remove lifecycle stale

[tenzen-y]

/remove-lifecycle stale