Define ClusterQueueSnapshot and CohortSnapshot types

[gabesaba]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Preparation for #79. Create Snapshot types for CQ and Cohort, to better differentiate between Cache types. We were currently relying on fields properly being set/copied, and some fields not being set.

This change will make the code easier to understand and less error prone.

Special notes for your reviewer:

Unexporting Cohort/ClusterQueue works trivially. I will send this out in a subsequent PR.

Additionally, I didn't move methods that operate on ClusterQueueSnapshot to the new file, to keep the diff smaller. These can be moved in a subsequent PR if we wish.

Also folding https://github.com/kubernetes-sigs/kueue/pull/2489 into this change.

Does this PR introduce a user-facing change?

NONE

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[alculquicondor]

/lgtm /approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: bd1d46818c682fcf6721ec4be56300a0d8cbd825

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alculquicondor, gabesaba

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[mimowo]

/test pull-kueue-test-e2e-main-1-28 /test pull-kueue-test-e2e-main-1-30 Looks like overloaded infra: "There are no nodes that your pod can schedule to - check your requests, tolerations, and node selectors" link