fix: adding "since" annotation to k8s nodes

[MenD32]

What type of PR is this?

/kind bug

What this PR does / why we need it:

Fixes bug where upon deployment restart, cluster-autoscaler resets the the node scaledown timer, which can cause nodes to never scale in extreme cases.

Which issue(s) this PR fixes:

Fixes #7873

Special notes for your reviewer:

this issue has already affected me, and I'm highly motivated to fix this ASAP. so I should be available during the next few days, in order to resolve this quickly. if you have a better way of fixing this HA issue, please suggest one 😄

Does this PR introduce a user-facing change?

Fixed: Cluster Autoscaler now persists scale-down cooldowns across pods. cooldown timestamps were stored in memory, causing inconsistencies when the original cluster autoscaler pod becomes unavailable. Now, cooldown state is stored as node annotations:

"cluster-autoscaler.kubernetes.io/unneeded" ("true"/"false")
"cluster-autoscaler.kubernetes.io/unneeded-since" (RFC3339 timestamp)

This ensures consistent scale-down behavior even if the original pod becomes unavailable.

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

[k8s-ci-robot]

Hi @MenD32. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: MenD32
Once this PR has been reviewed and has the lgtm label, please assign feiskyer for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• cluster-autoscaler/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment