[Documentation] Add XGBoostJob and Argo Workflows to supported Katib Worker types

[andreyvelich]

/kind feature

After this PR: #1603 we should add XGBoostJob to the supported Katib Workers: https://www.kubeflow.org/docs/components/katib/overview/#worker-job.

[andreyvelich]

After this PR: #1605 we also support Argo Workflows.
We should update the docs also.