instancetype: preferredCPUTopology cleanups

[lyarwood]

/area instancetype

What this PR does

This PR introduces shorter preferredCPUTopology constants to make the API slightly easier for users:

• PreferSockets -> sockets
• PreferCores -> cores
• PreferThreads -> threads
• PreferSpread -> spread
• PreferAny -> any

The original constants are now deprecated and support will be dropped in a future version of the instancetype.kubevirt.io API with these values converted during upgrade and thus requiring no user actions.

It also adds missing admission validation for preferredCPUTopology to ensure only supported values are accepted. This includes validation of virtctl input when creating a preference manifest.

Fixes #

Why we need it and why it was done in this way

The following tradeoffs were made:

The following alternatives were considered:

Links to places where the discussion took place:

Special notes for your reviewer

Checklist

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Approvers are expected to review this list.

• 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

All `preferredCPUTopology` constants prefixed with `Prefer` have been deprecated and will be removed in a future version of the `instancetype.kubevirt.io` API.

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[lyarwood]

/sig api
/cc @alaypatel07

Would you mind taking a look at this from a sig-api point of view, specifically the deprecation of the preferFoo constants and the introduction and naming of the new foo constants?

[alaypatel07]

https://github.com/kubernetes/kubernetes/blob/fad52aedfcc14061cf20370be061789b4f3d97d9/staging/src/k8s.io/api/core/v1/types.go#L3667

Kubernetes adds Depracated prefix to the api fields without changing the values. Should we follow this pattern here?

cc @EdDev

[0xFelix]

Should/Can we add a deprecation notice for users in the admitter?