Updated CRs documentation to include comment about istio annotation

[jdcfd]

Based on the discussion on the PR https://github.com/kubeflow/training-operator/pull/2004 , I updated the documentation website pages for the different *Job CRs to include a comment about having to disable automatic sidecar injection in some cases, and how to do that.

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[jdcfd]

Thanks @andreyvelich . I added the changes and signed off on the commit.

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: andreyvelich, jdcfd

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