Implement simple endpoint slice batching

[mborsz]

What type of PR is this?
/kind feature

What this PR does / why we need it:
This PR implements a simple endpoint slice batching. This tries to copy logic from #80509 to endpoint slice controller.

Those changes are disabled by default.
Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

New flag --endpointslice-updates-batch-period in kube-controller-manager can be used to reduce number of endpointslice updates generated by pod changes.

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

/assign @lavalamp

[fejta-bot]

This PR may require API review.

If so, when the changes are ready, complete the pre-review checklist and request an API review.

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[lavalamp]

/approve

OK from API and design perspective. Looks like the verify test is angry and a release note is needed, you can get an lgtm from anyone once you fix that.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lavalamp, mborsz

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Needs approval from an approver in each of these files:

• api/OWNERS [lavalamp]
• cmd/kube-controller-manager/OWNERS [lavalamp]
• pkg/controller/endpointslice/OWNERS [lavalamp]
• staging/src/k8s.io/kube-controller-manager/config/OWNERS [lavalamp]

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[mm4tt]

/lgtm

Thanks @mborsz and @lavalamp!