Pass DatadogAgent spec through managed EKS installation intents

[fanny-jiang]

What does this PR do?

Adds a v2 managed EKS Agent installation intent that can carry a partial or complete DatadogAgentSpec.

The Operator strictly decodes the supplied spec using the DDA API version bundled with the add-on, preserves managed cluster identity, credentials, and Linux scheduling settings, and rejects equivalent managed environment variable overrides. Existing v1 intents remain supported.

The EKS add-on configuration schema exposes a stable datadogAgent.spec envelope without duplicating the complete DDA CRD schema.

Motivation

Managed EKS installation needs a feature-agnostic way for the onboarding service to supply product-owned DDA defaults. This avoids adding a new intent field and Marketplace schema change for each DDA feature.

Tracking: https://datadoghq.atlassian.net/browse/TON-931

Additional Notes

The onboarding service must emit v2 only after selecting an add-on version containing this support. Existing v1 installations are not migrated automatically.

Corresponding dd-source change: https://github.com/ddoghq/dd-source/pull/99364

Minimum Agent Versions

No additional minimum Datadog Agent or Cluster Agent version.

Describe your test plan

• go test ./pkg/fleet/
• go vet ./pkg/fleet/
• git diff --check
• Validate that v1 intents remain accepted.
• Validate v2 DDA spec decoding, managed-field rejection, bootstrap ownership, normalized digest behavior, and uninstall handling.
• Validate the EKS add-on schema JSON and render the wrapper chart with a nested DDA spec.

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-datadog-prod-us1]

🎯 Code Coverage (details)
• Patch Coverage: 91.80%
• Overall Coverage: 51.30% (+0.07%)

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