feat: Support extra labels for bindplane and prometheus pods

[jsirianni]

Description of Changes

Added two new options

• extraPodLabels
• prometheus.extraPodLabels

These will add abitrary labels to the StatefulSet / Deployment's pod template (spec.template.metadata.labels, AKA pod labels).

Testing

minikube start
helm template charts/bindplane --values test/cases/labels/values.yaml | kubectl apply -f -

Once deployed, you can do a get pod <name on the bindplane and Prometheus pods, parse with jq.

➜  bindplane-op-helm git:(feat/extra-pod-labels) ✗ kubectl get pod release-name-bindplane-0 -o json | jq '.metadata.labels'
{
  "app.kubernetes.io/component": "server",
  "app.kubernetes.io/instance": "release-name",
  "app.kubernetes.io/name": "bindplane",
  "app.kubernetes.io/stack": "bindplane",
  "controller-revision-hash": "release-name-bindplane-69d7695dff",
  "extraKey": "extraValue",
  "extraKey2": "extraValue2",
  "statefulset.kubernetes.io/pod-name": "release-name-bindplane-0"
}

➜  bindplane-op-helm git:(feat/extra-pod-labels) ✗ kubectl get pod release-name-bindplane-prometheus-0 -o json | jq '.metadata.labels'
{
  "app.kubernetes.io/component": "prometheus",
  "app.kubernetes.io/instance": "release-name",
  "app.kubernetes.io/name": "bindplane",
  "app.kubernetes.io/stack": "bindplane",
  "controller-revision-hash": "release-name-bindplane-prometheus-564456c78b",
  "extraKeyProm": "extraValueProm",
  "extraKeyProm2": "extraValueProm2",
  "statefulset.kubernetes.io/pod-name": "release-name-bindplane-prometheus-0"
}

The labels defined in the values file appear on the pod as expected.

Please check that the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• CI passes