ServiceMonitor should allow specifying custom labels so that prometheus-operator can discover them

[AshutoshNirkhe]

Describe the feature you would like and why you want it
Currently ServiceMonitor template has fixed set of labels and doesn't allow specifying additional labels. If we allow specifying that, then existing prometheus-operator that are configured to discover ServiceMonitors based on some label will work fine. As of now, we have to disable ServiceMonitor template and deploy custom one with the matching label(which our prometheus-operator uses).

Additional context
Add any other context or screenshots about the feature request here.

additional_labels should be a map of additional labels, which can be inserted in template ar at runtime.

Something on these lines,

apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  labels:
    app: {{ template "kuberhealthy.name" . }}
    prometheus: {{ .Values.prometheus.name }}
    release: {{ .Values.prometheus.release }}
    {{ .Values.prometheus.serviceMonitor.additional_labels }}
  name: {{ template "kuberhealthy.name" . }}
  namespace: {{ .Release.Namespace }}

[integrii]

Makes sense... It looks like we need an additional set of labels supplied here and then here on the Kuberhealthy service.

[AshutoshNirkhe]

Sorry for bugging @joshulyne @integrii on this, but 'additionalLabels' key shouldn't be present in servicemonitor template. Its only required in values.yaml for input.

{{- if .Values.prometheus.additionalLabels}} 
additionalLabels: {{ .Values.prometheus.additionalLabels | nindent 6}} 
{{- end }}

should be updated to,

{{- if .Values.prometheus.additionalLabels}} 
{{ .Values.prometheus.additionalLabels | nindent 6}} 
{{- end }} 

[zjhans]

This was already fixed in #962
Closing.