Dashboards: Make the home dashboard non-editable (by default) (#68044)

public/dashboards/home.json

@@ -62,6 +62,7 @@
     "from": "now-6h",
     "to": "now"
   },
+  "editable": false,
   "timepicker": {
     "hidden": true,
     "refresh_intervals": ["5s", "10s", "30s", "1m", "5m", "15m", "30m", "1h", "2h", "1d"],