[CASCL-1386] (7/11) Evict EKS managed node groups

[L3n41c]

What does this PR do?

Implements EKS managed node group eviction (scale-to-zero then wait; EKS drains pods server-side, so it needs no client-side drain primitives).

Motivation

PR #3026 is too large to review as a single change. This is part 7 of 11 of a stack that splits it into small, individually-reviewable pieces that each build and pass tests on their own. See #3026 for the full feature context and end-to-end QA.

Additional Notes

Stacked PR — the base branch is lenaic/CASCL-1386-evict-06-ec2-instance-id-helper, not main, so the diff shows only this step's change. Implements an evictor the skeleton (part 1) left stubbed. The code is taken verbatim from #3026 (rebased onto main); there are no logic changes versus #3026.

Minimum Agent Versions

N/A — kubectl-datadog plugin only.

Describe your test plan

go test ./cmd/kubectl-datadog/autoscaling/cluster/... passes at this commit. Full end-to-end QA is tracked on #3026.

Checklist

• PR has at least one valid label
• qa/skip-qa label applied (not independently shippable; QA tracked on [CASCL-1386] Add evict-legacy-nodes subcommand to drain non-Datadog node groups #3026)
• All commits are signed

[datadog-prod-us1-4]

🎯 Code Coverage (details)
• Patch Coverage: 94.87%
• Overall Coverage: 44.35% (+0.07%)

_{This comment will be updated automatically if new data arrives.
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[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.11%. Comparing base (06f31c4) to head (8e43ad1).

Files with missing lines	Patch %	Lines
...bectl-datadog/autoscaling/cluster/evict/eks_mng.go	95.00%	2 Missing ⚠️

Additional details and impacted files

@@                                  Coverage Diff                                  @@
##           lenaic/CASCL-1386-evict-06-ec2-instance-id-helper    #3174      +/-   ##
=====================================================================================
+ Coverage                                              44.04%   44.11%   +0.07%     
=====================================================================================
  Files                                                    389      389              
  Lines                                                  31080    31119      +39     
=====================================================================================
+ Hits                                                   13690    13729      +39     
  Misses                                                 16498    16498              
  Partials                                                 892      892              

Flag	Coverage Δ
unittests	44.11% <95.00%> (+0.07%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...bectl-datadog/autoscaling/cluster/evict/eks_mng.go	95.12% <95.00%> (+95.12%)	⬆️

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