It's all done with a single-template Helm chart, with a seperate folder containing just a bunch of .json files:
{{- $files := .Files.Glob "dashboards/**.json" }}
{{- range $path, $fileContents := $files }}
{{- $dashboardName := regexReplaceAll "(.*)\\.json$" (base $path) "${1}" }}
{{- $dashboardFolder := (dir $path) }}
apiVersion: v1
kind: ConfigMap
metadata:
  namespace: monitoring
  name: camnet-{{ $dashboardName }}
  annotations:
    k8s-sidecar-target-directory: /tmp/{{ $dashboardFolder }}
  labels:
    grafana_dashboard: "1"
    camnet.site/checksum: {{ $.Files.Get $path | sha1sum }}
data:
  {{ $dashboardName }}.json: |
{{ $.Files.Get $path | indent 4 }}
---
{{- end }}