[CASCL-1386] (10/11) Evict Karpenter user NodePools

[L3n41c]

What does this PR do?

Implements Karpenter user NodePool eviction: cordon and drain (Karpenter reclaims the emptied instances).

Motivation

PR #3026 is too large to review as a single change. This is part 10 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-09-standalone, not main, so the diff shows only this step's change. Reuses the drain primitives introduced in part 8. 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-datadog-prod-us1-2]

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⚠️ Warnings

🚦 2 Pipeline jobs failed

DataDog/datadog-operator | unit_tests     

validation | build     

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.42%. Comparing base (a29e4e3) to head (f21be8d).

Files with missing lines	Patch %	Lines
...atadog/autoscaling/cluster/evict/karpenter_user.go	71.42%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@                            Coverage Diff                            @@
##           lenaic/CASCL-1386-evict-09-standalone    #3177      +/-   ##
=========================================================================
+ Coverage                                  44.41%   44.42%   +0.01%     
=========================================================================
  Files                                        391      391              
  Lines                                      31316    31322       +6     
=========================================================================
+ Hits                                       13908    13914       +6     
+ Misses                                     16509    16508       -1     
- Partials                                     899      900       +1     

Flag	Coverage Δ
unittests	44.42% <71.42%> (+0.01%)	⬆️

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

Files with missing lines	Coverage Δ
...atadog/autoscaling/cluster/evict/karpenter_user.go	75.00% <71.42%> (+75.00%)	⬆️

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