promote PodNodeSelector admission controller annotations to stable

[colemickens]

What this PR does / why we need it:

• promotes the PodNodeSelector admission controller and annotations to stable, per discussion on PodNodeSelector and PodTolerationRestriction feature status is unclear #57424
• deprecates the alpha annotation (scheduler.alpha.kubernetes.io/node-selector) but supports it simultaneously with the new annotation (scheduler.kubernetes.io/node-selector), again per discussion on PodNodeSelector and PodTolerationRestriction feature status is unclear #57424
• adds tests showing the alpha and stable annotations are merged and considered correctly
• moves the parsing of the config files node selector into plugin initialization
• adds api validation checks for the pod node selector values
• introduces versioned configuration for PodNodeSelector plugin

(Note: it intentionally drops support for the alpha configuration format due to some discussed potential concerns about incorrectly parsing legacy configuration in a way that leaves the cluster mistakenly open in some way. The format also was just undesirable due to effectively being a map with a special-cased key.)

Which issue(s) this PR fixes: Partially addresses #57424 (the other half, addressing PodTolerationRestriction will follow this PR).

Corresponding Docs PR: kubernetes/website#7134 (This will be updated again to discuss the versioned config, etc).

Release note:

* PodNodeSelector: `scheduler.alpha.kubernetes.io/node-selector` is deprecated in favor of `scheduler.kubernetes.io/node-selector`
* PodNodeSelector: support for alpha configuration format is removed. support for v1 configuration is added.

cc: @ericchiang @liggitt

[ericchiang]

Flaking on #59426

/test pull-kubernetes-unit

[colemickens]

/sig api-machinery

[lavalamp]

Stable features should not be using annotations like this, I think. Has this been debated?

[lavalamp]

Why is this api machinery?

[wanghaoran1988]

/sig scheduling

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[adampl]

Hi, what about this issue? Has it been sorted out?

[pierluigilenoci]

@colemickens what happened to this PR?

[adampl]

@colemickens reopen?

[adampl]

@liggitt Please reopen if it makes sense.