chore: add node-exporter validation before version bump

[chmill-zz]

What this does

• parses the node-exporter scrape as Prometheus exposition data instead of checking for any node_ text
• validates every node-exporter metric family retained by the AKS default Prometheus profile
• verifies the service is persistently enabled and remains active after scraping
• adds focused unit coverage for valid and missing metric families

Why

Node-exporter is currently pinned to 1.9.1 and PMC now carries 1.12.1. This establishes the existing metrics contract before taking the multi-minor version update in a separate PR.

Validation

• go test . -run TestValidateNodeExporterMetrics
• go test . -run ^
• go test ./components
• go vet .
• git diff --check

[Copilot]

Pull request overview

This PR strengthens the AgentBaker e2e validation for node-exporter by treating the scrape output as Prometheus exposition format and asserting the presence of specific metric families that represent the AKS default Prometheus scraping contract, establishing a baseline before a future node-exporter version bump.

Changes:

• Parse /metrics output using Prometheus text exposition parsing and validate a fixed set of required metric families.
• Tighten the systemd enablement check to require a persistently enabled unit state and verify the service stays active after scraping.
• Add unit tests covering valid metrics text and a missing-required-metric failure case.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
e2e/validators.go	Reworks node-exporter e2e validation to parse Prometheus exposition format and validate required metric families; adds post-scrape service health check.
e2e/validators_node_exporter_test.go	Adds focused unit tests for the node-exporter metrics validation helper.
e2e/go.mod	Adds github.com/prometheus/common dependency to support exposition parsing.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.