feat: add servicemonitor additonal labels

[ckav370]

what

Add additional Kubernetes labels to the ServiceMonitor as this is often required by the Prometheus operator to identify the Service and pod(s).

why

The current configuration does not support adding labels to the Service Monitor. To add these labels in the case of adding a label for the Prometheus Operator, kustomize can be used or maintaining a separate resource for ServiceMonitor which is unnecessarily complex.

tests

Helm templates with servicemonitor.enabled set to true with test additionalLabels

servicemonitor:
  # to enable a Prometheus servicemonitor, set enabled to true,
  #   and enable the metrics in this file's repoConfig
  #   by setting a value for metrics.prometheus.endpoint
  enabled: true
  interval: "30s"
  path: /metrics
  # Prometheus ServiceMonitor labels
  additionalLabels:
    test-label: test

---
# Source: atlantis/templates/servicemonitor.yaml
apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  name: release-name-atlantis
  labels:
    app: atlantis
    chart: atlantis-4.21.0
    helm.sh/chart: atlantis-4.21.0
    release: release-name
    heritage: Helm
    test-label: test
spec:
  selector:
    matchLabels:
      app: atlantis
      chart: atlantis-4.21.0
      helm.sh/chart: atlantis-4.21.0
      release: release-name
      heritage: Helm
  namespaceSelector:
    matchNames:
     - default
  endpoints:
  - port: atlantis
    interval: 30s
    path: /metrics

references

#353 -> Link to a Issue :)

[GMartinez-Sisti]

Thanks @cblaindnsf !