[grafana] container dashboard make them more portable

[DrummyFloyd]

Describe the enhancement you are proposing:

Because many user have already there own stack, and don't want to install dedicated stack... but want to reuse predefined dashboards created by CrunchyData would be appreciated to have a better used of

{
  "__inputs": [
    {
      "name": "DS_PROMETHEUS",
      "label": "PROMETHEUS",
      "description": "",
      "type": "datasource",
      "pluginId": "prometheus",
      "pluginName": "Prometheus"
    }
  ],

old HARDCODED(using labels)

  "panels": [
    {
      "datasource": "PROMETHEUS",
      "fieldConfig": {
...

New based on __inputs

  "panels": [
    {
      "datasource": "${DS_PROMETHEUS}",
      "fieldConfig": {
        "defaults": {
          "color": {
            "mode": "thresholds"
          },