docs: WorkloadEncryptionSEV Alpha -> Beta Graduation

[alancaldelas]

What this PR does / why we need it:
Update user guide for SEV Alpha to Beta graduation, informing users as of v1.9 this feature is enabled by default.

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 #

Special notes for your reviewer:
PRs:

• WorkloadEncryptionSEV Alpha -> Beta graduation kubevirt#18048 (WorkloadEncyptionSEV Alpha -> Beta Graduation)

Checklist

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• Design: A design document was considered and is present (link) or not required
• PR: The PR description is expressive enough and will help future contributors
• Code: Write code that humans can understand and Keep it simple
• Refactor: You have left the code cleaner than you found it (Boy Scout Rule)
• 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
• 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:

WorkloadEncryptionSEV Alpha -> Beta graduation docs updated

[kubevirt-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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• docs/cluster_admin/OWNERS

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[aburdenthehand]

/lgtm
Thanks for the catch @alancaldelas !

[alancaldelas]

/assign iholder101

Hi @iholder101 — this one has an lgtm from @aburdenthehand and just needs an approver for docs/cluster_admin/OWNERS. It's a docs-only follow-up to kubevirt/kubevirt#18048 (merged), updating the SEV / SEV-SNP feature state for the WorkloadEncryptionSEV Alpha -> Beta graduation. PTAL, thanks!

[kubevirt-bot]

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