Restore runner name label in listener metrics

[air-hand]

This PR restores the runner_name label to job metrics as an opt-in feature for inspect pod performance issue purpose.
The label can be enabled by configuring it in the metrics configuration.

Also adds unit tests that maintain existing structure and avoid complex mocking.

Origin: https://github.com/orgs/community/discussions/167243

[Copilot]

Pull Request Overview

This PR restores the runner_name label to job metrics as an opt-in feature that can be enabled through metrics configuration. The change addresses a community request to include runner identification in metrics for better observability.

• Adds runner_name label to job completion and startup metrics
• Refactors label filtering logic by extracting a reusable helper function
• Updates configuration examples to demonstrate the new optional label

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
cmd/ghalistener/metrics/metrics.go	Adds runner_name label constant, updates job label methods to include runner name, and refactors label filtering into a helper function
cmd/ghalistener/metrics/metrics_test.go	Adds comprehensive unit tests for the new label functionality and helper function
charts/gha-runner-scale-set/values.yaml	Updates commented configuration examples to include the new runner_name label option

[Copilot]

The test relies on implementation details by setting Metrics to nil and expecting specific behavior. Consider using a more explicit test setup that doesn't depend on nil handling.

Suggested change

	Metrics: nil, // when metrics is nil, all default metrics should be registered
	Metrics: NewDefaultMetrics(), // explicitly use default metrics implementation

[Copilot]

The test relies on implementation details by setting Metrics to nil and expecting specific behavior. Consider using a more explicit test setup that doesn't depend on nil handling.

Suggested change

	Metrics: nil, // when metrics is nil, all default metrics should be registered
	Metrics: NewDefaultMetrics(), // explicitly configure default metrics

[air-hand]

@nikola-jokic
Hi nikola.
No rush, but would appreciate feedback when convenient plz.