Add autoscaling failover config to DatadogAgent CR

[clamoriniere]

What does this PR do?

Adds a new failover.enabled boolean option under spec.features.autoscaling.workload in the DatadogAgent CR to control the autoscaling failover mechanism. When enabled (the default), the operator automatically sets DD_AUTOSCALING_FAILOVER_ENABLED and DD_AUTOSCALING_FAILOVER_METRICS environment variables on the Cluster Agent and Node Agent components.

Motivation

Previously, users who enabled workload autoscaling had to manually add DD_AUTOSCALING_FAILOVER_ENABLED environment variable overrides to both clusterAgent and nodeAgent sections. This change makes failover a first-class configuration option that is enabled by default when workload autoscaling is active, removing the need for manual env var overrides.

Additional Notes

The failover is enabled by default (true) when workload autoscaling is enabled. Users can explicitly disable it:

spec:
  features:
    autoscaling:
      workload:
        enabled: true
        failover:
          enabled: false

Minimum Agent Versions

• Agent: N/A
• Cluster Agent: N/A

Describe your test plan

• Unit tests updated and extended with two new test cases: explicit failover enabled and failover disabled
• All 7 tests pass
• go vet and gofmt clean
• CRD, deepcopy, and OpenAPI schemas regenerated

Checklist

• PR has at least one valid label: bug, enhancement, refactoring, documentation, tooling, and/or dependencies
• PR has a milestone or the qa/skip-qa label
• All commits are signed (see: signing commits)

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[datadog-prod-us1-3]

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Bits Dev status: ✅ Done

CI Auto-fix: Disabled | Enable

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[datadog-prod-us1-3]

I can only run on private repositories.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 38.81%. Comparing base (a2fb04f) to head (0c544aa).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2723   +/-   ##
=======================================
  Coverage   38.81%   38.81%           
=======================================
  Files         308      308           
  Lines       26705    26707    +2     
=======================================
+ Hits        10365    10367    +2     
  Misses      15561    15561           
  Partials      779      779           

Flag	Coverage Δ
unittests	38.81% <100.00%> (+<0.01%)	⬆️

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

Files with missing lines	Coverage Δ
...roller/datadogagent/feature/autoscaling/feature.go	84.61% <100.00%> (+0.40%)	⬆️

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[tbavelier]

Discussing offline so "blocking" the PR until then: failover was already always enabled when configured with the operator. Metrics env var was only added on node Agent, not on DCA

[clamoriniere]

Ok, when I checked that it was missing,it was indeed in the cluster-agent
Still we need to give a way to disable it in some cases.
I will update the PR