Introduce a plugin mechanism for arbitrary checks during workload admission.

[mwielgus]

What would you like to be added:

A mechanism to admit workloads based on both ClusterQueue quota and checks made by an external controller.

Why is this needed:

The current admission process only checks queue resources and doesn't allow to use some cloud provider API or prometheus database query.

Completion requirements:

This enhancement requires the following artifacts:

• Design doc
• API change
• Docs update

The artifacts should be linked in subsequent comments.

[alculquicondor]

/reopen
Implementation is still ongoing

[k8s-ci-robot]

@alculquicondor: Reopened this issue.

In response to this:

/reopen
Implementation is still ongoing

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[trasc]

/assign