image field in hook sidecar annotation is optional

[tiraboschi]

What this PR does / why we need it: with https://github.com/kubevirt/kubevirt/pull/11272 image field becomes optional in the hook sidecar annotation since, if omitted, virt-controller will now use a default sidecar-shim image built with other kubevirt images.

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 #775

Special notes for your reviewer: No to retrieve the version of the hook sidecar shim version from kubevirt CR, the virt-controller can now autonomously handle it.

Checklist

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• [X] Design: A design document was considered and is present (link) or not required
• [X] PR: The PR description is expressive enough and will help future contributors
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• [X] Upgrade: Impact of this change on upgrade flows was considered and addressed if required
• [ ] Testing: New code requires new unit tests. New features and bug fixes require at least on e2e test
• [X] Documentation: A user-guide update was considered and is present (link) or not required. You want a user-guide update if it's a user facing feature / API change.
• [ ] Community: Announcement to kubevirt-dev was considered

Release note:

image field in hook sidecar annotation is optional

[alicefr]

/approve

[alicefr]

/lgtm

[kubevirt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alicefr, phoracek

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