add stand alone pod annotation check in pod webhook

[BenHinthorne]

What type of PR is this?

/kind feature

This PR adds a check for a "kueue.x-k8s.io/standalone" annotation on plain pods. If this annotation exists, then these pods will be suspended even if their ownerReference is a known integration to Kueue.

Only a draft for now.

What this PR does / why we need it:

At a high level, this would give users more flexibility to process plain pods with Kueue. Currently, users are blocked from allowing Kueue to process any pods that are owned by a known integration to Kueue.

For example, in Spark Apps, the Driver Pod is the Owner of the Executor pods. This prevents the Executor pods from being processed by Kueue at all, because the pod_webhook sees that they are owned by a resource of "Kind: Pod". With this annotation, users would be able to process these executors as plain pods. See the linked issue for more details.

Which issue(s) this PR fixes:

Fixes # #4106

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Add support for pods annotated with `kueue.x-k8s.io/standalone` to be suspended and have a workload created for them regardless of their ownerReference being a known Kueue integration. 

[k8s-ci-robot]

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[k8s-ci-robot]

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