Implement metadata injection inside operator

[ramkrishankumarN]

Description

(https://newrelic.atlassian.net/wiki/spaces/KOT/pages/5428150500/Using+k8s+agent+operator+for+Metadata+Injection)
Problem Statement
New Relic currently maintains two separate Kubernetes operators:

k8s-metadata-injection: Injects Kubernetes metadata (cluster, node, namespace, pod, container names) as environment variables to enable APM-to-infrastructure correlation

k8s-agents-operator: Auto-instruments pods with New Relic APM agents via init containers

Maintaining two separate webhooks creates operational complexity, potential conflicts, and duplicated effort. Especially with trivy tickets and other update related to go packages.

This project consolidates both functionalities into the k8s-agents-operator, allowing customers to use a single operator for both metadata injection and agent instrumentation.

User Requirements
Opt-in model: Metadata injection disabled by default, explicitly enabled via environment variable

Environment variable configuration: Cluster name configured via K8S_CLUSTER_NAME environment variable

Complete replacement: k8s-metadata-injection repository will be deprecated after this implementation

Backward compatibility: Existing agent injection functionality must remain unchanged

Namespace filtering: Support ignore lists and label-based filtering

Independent operation: Metadata injection should work with or without agent injection

Metadata Environment Variables
The following 7 environment variables will be injected (matching k8s-metadata-injection):

NEW_RELIC_METADATA_KUBERNETES_CLUSTER_NAME (from config)
NEW_RELIC_METADATA_KUBERNETES_NODE_NAME (downward API: spec.nodeName)
NEW_RELIC_METADATA_KUBERNETES_NAMESPACE_NAME (downward API: metadata.namespace)
NEW_RELIC_METADATA_KUBERNETES_POD_NAME (downward API: metadata.name)
NEW_RELIC_METADATA_KUBERNETES_DEPLOYMENT_NAME (derived from generateName)
NEW_RELIC_METADATA_KUBERNETES_CONTAINER_NAME (static: container name)
NEW_RELIC_METADATA_KUBERNETES_CONTAINER_IMAGE_NAME (static: container image)
Architecture Approach
New PodMutator Implementation
Create a separate MetadataInjectionPodMutator that implements the existing PodMutator interface. This provides:

Clean separation of concerns (metadata vs agent injection)

Ability to enable/disable independently

Runs first in the mutator chain (before agent injection)

No CRD dependencies (configuration via environment variables only)

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• New feature / enhancement (non-breaking change which adds functionality)
• Security fix
• Bug fix (non-breaking change which fixes an issue)

Checklist:

• Documentation has been updated
• This change requires changes in testing:
  • unit tests
  • E2E tests

[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 12.72727% with 144 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.11%. Comparing base (5189aac) to head (8656cea).

Files with missing lines	Patch %	Lines
internal/metadata/mutator.go	0.00%	107 Missing ⚠️
internal/webhook/podmutationhandler.go	51.72%	11 Missing and 3 partials ⚠️
internal/metadata/config.go	33.33%	10 Missing and 2 partials ⚠️
cmd/main.go	0.00%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #556      +/-   ##
==========================================
- Coverage   68.74%   66.11%   -2.64%     
==========================================
  Files          53       55       +2     
  Lines        3513     3665     +152     
==========================================
+ Hits         2415     2423       +8     
- Misses        863     1002     +139     
- Partials      235      240       +5     

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