feat(helm): add configurable relabelings to PodMonitor resources

[bezarsnba]

Problem

The current PodMonitor templates have hardcoded metricRelabelings that cannot be customized. This prevents users from:

• Adding organizational labels for cost allocation and compliance
• Reducing metric cardinality to control storage costs

Somes scenarios require custom metric labels to meet regulatory compliance or internal governance policies.

Solution

Add new configuration options to the Helm chart:

• podMonitor.*.metricRelabelings - Replace default relabelings entirely
• podMonitor.*.additionalRelabelings - Extend existing relabelings

Changes Made

• Updated podmonitor.yaml template to support configurable relabelings
• Added new fields to values.yaml with documentation and examples
• Created comprehensive test scenarios in debug.values.yaml
• Maintained full backward compatibility

Example Usage

podMonitor:
  # Enable PodMonitor creation
  enabled: true

  # Global PodMonitor settings
  scrapeInterval: "15s"
  scrapeTimeout: "10s"
  controller:
    enabled: true
    namespaceSelector: |
      matchNames:
        - {{ .Release.Namespace }}
        - linkerd-viz
    metricRelabelings:
      - sourceLabels: [__name__]
        regex: 'controller_.*_duration_seconds_bucket'
        action: drop
    additionalRelabelings:
      - sourceLabels: [__meta_kubernetes_pod_label_environment]
        targetLabel: environment
        action: replace
      - action: labeldrop
        regex: 'pod_template_hash|controller_revision_hash'

  serviceMirror:
    enabled: true
    metricRelabelings:
      - sourceLabels: [__name__]
        regex: 'service_mirror_.*_errors_total'
        action: drop

    additionalRelabelings:
      - sourceLabels: [__meta_kubernetes_pod_label_source_cluster]
        targetLabel: source_cluster
        action: replace

  proxy:
    enabled: true
    metricRelabelings:
      - sourceLabels: [le]
        regex: '2\.[0-9]+|3\.[0-9]+|4\.[0-9]+|5\.[0-9]+'
        action: drop
    additionalRelabelings:
      - action: labeldrop
        regex: '__tmp_.*'
      - sourceLabels: [__meta_kubernetes_pod_label_pod_template_hash]
        targetLabel: deployment_generation
        action: replace

Testing

✅ Helm template renders correctly
✅ Deploys successfully to Kubernetes
✅ Prometheus processes custom relabelings
✅ Backward compatibility confirmed