Fix ExternalName service handling and add standardized owner kind mappings

[allanhung]

Summary

• Fix ExternalName service handling to return gracefully without error since they don't have pod selectors
• Add standardized service name mappings for Argo Workflow, Spark, and GitHub Actions runner workloads
• Add comprehensive test coverage for both fixes (5 new test cases)
• Improve code documentation with detailed comments explaining the rationale

Changes

ExternalName Service Fix (4 API versions)

• Modified ServiceIdentityToLabelsForWorkloadSelection in v1alpha3, v1beta1, v2alpha1, v2beta1
• ExternalName services now return (nil, false, nil) instead of throwing "service has no selector" error
• Added inline comments explaining why ExternalName services are handled specially

Standardized Owner Kind Mappings

• Workflow → argo-workflow: Consistent identity for Argo Workflow pods
• SparkApplication → spark: Groups Spark driver and executor pods
• RunnerDeployment → actions-runner: Consistent identity for GitHub Actions runners
• Service owners now include API group to prevent naming conflicts

Test Coverage

Added 5 new test cases in serviceidresolver_test.go:

1. TestServiceIdentityToPodLabelsForWorkloadSelection_ServiceKind_ExternalNameService
2. TestResolvePodToServiceIdentity_WorkflowOwner
3. TestResolvePodToServiceIdentity_SparkApplicationOwner
4. TestResolvePodToServiceIdentity_RunnerDeploymentOwner
5. TestResolvePodToServiceIdentity_ServiceOwner

All tests pass successfully.

Test plan

• Run unit tests: go test ./shared/serviceidresolver/... -v
• Verify ExternalName service handling test passes
• Verify owner kind mapping tests pass
• Code formatting with go fmt

🤖 Generated with Claude Code

[github-actions]

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- Name: Allan Hung
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[allanhung]

Closing this PR as it should be created in my fork repository instead.