Update Katib Experiment Workflow Guide

[andreyvelich]

What you would like to be added?

We move this sequence diagram to the Kubeflow Katib reference guides: https://github.com/kubeflow/katib/blob/master/docs/workflow-design.md#what-happens-after-an-experiment-cr-is-created.

After that, we should remove this doc from the Katib repository.

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[andreyvelich]

/good-first-issue

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