Generate Configmap for each dashboard json based on file name.

configmap-ds1.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: dashboard
  labels:
    grafana_dashboard: 1
data:
  dashboard.json: |
    {
      "id": null,
      "uid": "cLV5GDCkz",
      "title": "New dashboard",
      "tags": [],
      "style": "dark",
      "timezone": "browser",
      "editable": true,
      "hideControls": false,
      "graphTooltip": 1,
      "panels": [],
      "time": {
        "from": "now-6h",
        "to": "now"
      },
      "timepicker": {
        "time_options": [],
        "refresh_intervals": []
      },
      "templating": {
        "list": []
      },
      "annotations": {
        "list": []
      },
      "refresh": "5s",
      "schemaVersion": 17,
      "version": 0,
      "links": []
    }

dashboard.json

{
  "id": null,
  "uid": "cLV5GDCkz",
  "title": "New dashboard",
  "tags": [],
  "style": "dark",
  "timezone": "browser",
  "editable": true,
  "hideControls": false,
  "graphTooltip": 1,
  "panels": [],
  "time": {
    "from": "now-6h",
    "to": "now"
  },
  "timepicker": {
    "time_options": [],
    "refresh_intervals": []
  },
  "templating": {
    "list": []
  },
  "annotations": {
    "list": []
  },
  "refresh": "5s",
  "schemaVersion": 17,
  "version": 0,
  "links": []
}

gen-configmap-dashboards.sh

#!/bin/bash

# pick script dir
here=$(cd $(dirname $0); pwd)

# dashboard counter
i=1

# increment counter
function incrementCounter() {
  ((i=i+1))
}
# replace space to - for k8s name restriction
function string:replaceSpace() {
  echo "${1}" | sed "s/ /${2}/g"
}
function path:getFiles() {
  (cd "${here}" && ls ${1} | cat)
}
# pick filename w/o extensions
function file:getName() {
  echo "${1%.*}" | sed "s/ /-/g"
}
# add indent
function file:addIndentEachline() {
  cat "${here}/${1}" | sed 's/^/    /g'
}

function genConfigmap() {
  local file="${1}"
  local replaced=$(string:replaceSpace "${file}" "-")
  local name=$(file:getName "${replaced}")
  local json=$(file:addIndentEachline "${file}")
  cat <<EOF > "${here}/configmap-ds${i}.yaml"
apiVersion: v1
kind: ConfigMap
metadata:
  name: grafana-dashboard-${name}
  labels:
    grafana_dashboard: "1"
data:
  ${replaced}: |
${json}
EOF
}

# prepare
ORG_IFS=$IFS
IFS=$(echo -en "\n\b")

# gen
for file in $(path:getFiles "*.json"); do
  genConfigmap "${file}"
  incrementCounter
done

# restore
IFS=$ORG_IFS

run.sh

. ./gen-configmap-dashboards.sh

values.yaml

sidecar:
  dashboards:
    enabled: true

before

$ ls
dashboard.json gen-configmap-dashboards.sh

after

ls 
configmap-ds1.yaml dashboard.json gen-configmap-dashboards.sh

You should use Kustomization instead of this script.