Universal Operator Phase III: Graduate operator to production grade

[Jeffwan]

In Phase II #1299, we unified code structure and refactor all controller to have same operator pattern. In addition, we enabled test cases against dev branch and make sure original tests pass which makes us pretty confident to merge dev back to master.

In Phase III, we will prepare for the initial release. There're a few graduation criterions (kubeflow/common#138) need to be addressed before alpha release

1. Build new operator image release process as post-submit Prow job
2. Prepare tests against different frameworks (controllers)
3. Update kustomization manifests.
4. Json Logging support
5. Improve observability (liveness/readiness/job metrics)
6. API reference and Kubeflow website updates

/cc @kubeflow/wg-training-leads

[Jeffwan]

Feel free to pick up any issues if contributor has bandwidth.

[Jeffwan]

/priority p1

[Jeffwan]

Once all above issues are resolved. We should update README.md to ask user to use universal operators.

[Jeffwan]

For universal operator related stores are all done. some items need further improvement will be moved out from this epic. We can track their progress separately.