Strip managed fields from controller-runtime cache

[tbavelier]

What does this PR do?

Strips metadata.managedFields from objects before storing them in the controller-runtime cache.

Motivation

The operator does not inspect cached managed fields. The controller-runtime documentation notes that using this transform can significantly reduce cache memory usage. Live Kubernetes objects and field ownership are unchanged.

Additional Notes

The initial version also registered controller-runtime field indexes for the app.kubernetes.io/part-of label on resource types managed by the DatadogAgent reconcilers. Stale-resource cleanup then used client.MatchingFields to avoid scanning every cached object of each type.

Staging profiling on genesect and entei showed no consistent memory or CPU improvement, while reconcile p99 improved only on genesect and regressed on entei. The indexing changes were therefore removed to avoid the additional manager setup, fake-client wiring, and test complexity.

Minimum Agent Versions

• Agent: N/A
• Cluster Agent: N/A

Describe your test plan

Automated coverage verifies that the default cache transform removes managed fields. go test ./pkg/config and make lint pass.

QA: This will be tested in staging by validating normal reconciliation and cache behavior.

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)

[datadog-prod-us1-5]

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 47.75% (+0.00%)

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