Add AKS-owned labels to Flex Nodes

[Wenxuan W (wenxuan0923)]

Summary

• Add the AKS-managed, agent-pool, mode, and node-pool-type labels when building kubelet configuration.
• Keep those server-owned labels out of node.labels so Machine goals contain only custom labels.
• Reject configuration that attempts to set an AKS-owned label.

Validation

• make check

Context

This is the first independent replacement for draft PR #256.

[Copilot]

Pull request overview

This PR updates FlexNode kubelet label handling to ensure required AKS-managed labels are always applied at kubelet registration time, while preventing those AKS-owned keys from being specified as user/custom node.labels (so ARM Machine “custom labels” remain purely user-defined).

Changes:

• Add a dedicated label builder (kubeletNodeLabels) that merges custom labels with required AKS-owned labels for kubelet configuration.
• Remove the default injection of kubernetes.azure.com/managed=false into node.labels and instead apply it (and other AKS-owned labels) only when building kubelet labels.
• Add validation + tests to reject configs that attempt to set AKS-owned labels via node.labels.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
pkg/config/kubelet_config_test.go	Adds coverage for rejecting AKS-owned labels in node.labels.
pkg/config/config.go	Removes default managed label from node.labels and adds validation blocking AKS-owned labels.
pkg/config/adapter.go	Introduces AKS-owned label constants and builds kubelet labels via kubeletNodeLabels.
pkg/config/adapter_test.go	Adds/updates tests to assert kubelet labels include AKS-owned labels without mutating custom labels.

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[hbc (bcho)]

does AKS RP side process nodes with this agent pool label? Because this could be overrode by user

[Wenxuan W (wenxuan0923)]

Synced offline, this label is immutable after node creation.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.

Suppressed comments (1)

pkg/config/adapter.go:181

• The comment above the AKS-owned label additions is misleading: this function returns a label map that includes AKS-owned labels, so they are not being kept "out" of the returned labels. The real behavior is that cfg.Node.Labels (Machine custom labels) is not mutated; AKS-owned labels are added only for kubelet registration.

	// Keep AKS-owned labels out of the custom labels sent in the Machine goal.