feat: Replace endpoints with endpointslices as default resource

[mrueg]

What this PR does / why we need it:
BREAKING CHANGE: endpoints are not a default resource anymore and metrics need to be replaced with endpointslices' metrics.

https://kubernetes.io/blog/2025/04/23/kubernetes-v1-33-release/#deprecation-of-the-stable-endpoints-api.

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)
None
Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

[richabanker]

/triage accepted
cc @rexagod

[rexagod]

I see, this moves endpoints out of the default set of resources for which we generate metrics for, and users will need to use the --resources flag to re-enable it. While that makes sense, I'd suggest a couple of releases indicating this (in the change-log, at runtime if endpoints are present in --resources, etc.) to warn users.

It'd additionally make sense to put this behind a flag, and enable it by default once the deprecation deadline hits. This way, users can start opt-ing into the feature before it's dropped.

[CatherineF-dev]

/lgtm

/hold

Feel free to unhold

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CatherineF-dev, mrueg

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