[1.13] docs: Add `imageIndex` field to `imageData`

[NetanelK]

Related issue

Issue - kyverno/kyverno#8273 PR - kyverno/kyverno#9883

Proposed Changes

Add imageIndex to imageData documentation.

Checklist

• [X] I have read the contributing guidelines.
• [X] I have inspected the website preview for accuracy.
• [X] I have signed off my issue.

[welcome[bot]]

Thanks for opening your first Pull Request here! Please check out our Contributing guidelines and confirm that you Signed off.

[JimBugwadia]

@NetanelK - thanks for the contribution! Can you please resolve the conflict, so we can merge this?

[realshuting]

I can't push to the forked repo, created https://github.com/kyverno/website/pull/1182.

Thanks for sending the PR @NetanelK !