Add KEP for OptimizationJob CRD

[aniket2405]

What this PR does / why we need it:

This PR introduces the KEP for the OptimizationJob CRD, purpose-built for orchestrating Hyperparameter Optimization specifically for TrainJobs.

Doc Ref for KEP: https://docs.google.com/document/d/1Y8IJ-UdZ7VCEAlax_xEFbbqEi7EB6SfIX4D7ua-xn4M/edit?usp=sharing

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #2605

Checklist:

• Docs included if any changes are user facing
• KEP doc: https://docs.google.com/document/d/1Y8IJ-UdZ7VCEAlax_xEFbbqEi7EB6SfIX4D7ua-xn4M/edit?usp=sharing

[github-actions]

🎉 Welcome to the Kubeflow Katib repo! 🎉

Thanks for opening your first PR! We're excited to have you onboard 🚀

Next steps:

• Our team will review your PR soon! cc @kubeflow/wg-automl-leads
• Check out the Contributing Guide and the Kubeflow Contributor Guide
• Join the Kubeflow Slack channels: https://www.kubeflow.org/docs/about/community/#kubeflow-slack-channels
• Join the AutoML & Training WG meetings: https://bit.ly/2PWVCkV

Feel free to ask questions in the comments. Thanks again for contributing! 🙏

[google-oss-prow]

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[andreyvelich]

/ok-to-test