Avoid unnecessary preemptions when candidates have the same timestamp

[alculquicondor]

What type of PR is this?

/kind bug

What this PR does / why we need it:

When there are multiple workloads waiting for preemption and multiple candidates with the same timestamp, it was possible that all these candidates would be preempted across a few admission attempts.

This can be mitigated by using the information about the workloads pending preemption and introducing stable sorting.
In this fix, I'm using the UID as an arbitrary unpredictable key to do stable sorting.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Avoid unnecessary preemptions when there are multiple candidates for preemption with the same admission timestamp

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alculquicondor

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[alculquicondor]

/assign @yaroslava-serdiuk

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[yaroslava-serdiuk]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 7cb5e46dbb00b317e6e526b7a8f18e913baf9bbf

[alculquicondor]

/cherry-pick release-0.6

[k8s-infra-cherrypick-robot]

@alculquicondor: new pull request created: #1880

In response to this:

/cherry-pick release-0.6

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