[ci skip] Add Grafana dashboard for Technitium DNS query logs

Add MySQL datasource and 15-panel dashboard for DNS analytics:
queries over time, response codes, top domains/clients, response
times, blocked/NxDomain domains. Enable Grafana dashboard sidecar
for auto-provisioning dashboards from ConfigMaps.

modules/kubernetes/monitoring/grafana_chart_values.yaml

@@ -20,9 +20,8 @@ sidecar:
   datasources:
     enabled: "true"
   dashboards:
-    enabled: false
-    # label: "grafana_dashboard"
-    # folder: "/var/lib/grafana/dashboards"
+    enabled: true
+    label: "grafana_dashboard"
 dashboardProviders:
   dashboardproviders.yaml:
     apiVersion: 1