Cherry pick #3536 and #3547 to 0.8

[gabesaba]

Special notes for your reviewer:

I had to manually reimplement PotentiallyAvailable, as that was introduced with HierarchicalCohorts (0.9)

Does this PR introduce a user-facing change?

Change, and in some scenarios fix, the status message displayed to user when a workload doesn't fit in available capacity.
Determine borrowing more accurately, allowing preempting workloads which fit in nominal quota to schedule faster

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[mimowo]

/lgtm
/approve
Thanks!

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 55158586a7a73e3b57a1a8f15c5801face122253

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[mimowo]

/kind bug

[mimowo]

/release-note-edit

Change, and in some scenarios fix, the status message displayed to user when a workload doesn't fit in available capacity.
Determine borrowing more accurately, allowing preempting workloads which fit in nominal quota to schedule faster

It presents better in the release notes without the "-" prefix (as the release notes list adds one already).