Provides a base panel to construct the main dashboard

This patch adds a default panel that will be used when another service
will add a new panel into the main dashboard through grains. This is the
common part between all panels of the main dashboard.

It replaces the static main dashboard that has been removed.
diff --git a/metadata/service/client/single.yml b/metadata/service/client/single.yml
index 0f8aef7..62407e0 100644
--- a/metadata/service/client/single.yml
+++ b/metadata/service/client/single.yml
@@ -4,3 +4,65 @@
   grafana:
     client:
       enabled: true
+      base_templates:
+        main_dashboard:
+          title: 'Main'
+          editable: true
+          hideControls: false
+          templating:
+            enable: true
+            list:
+            - allFormat: regex values
+              hide: 0
+              includeAll: false
+              name: environment
+              options: []
+              query: show tag values from cpu_idle with key = environment_label
+              refresh: 1
+              refresh_on_load: true
+              regex: ''
+              type: query
+              sort: 0
+              multi: false
+        service_row:
+          showTitle: true
+          height: 100px
+        cluster_status_singlestat:
+          span: 2
+          editable: false
+          type: singlestat
+          prefixFontSize: "50%"
+          postfixFontSize: "50%"
+          colorBackground: true
+          colors:
+            - "rgba(71, 212, 59, 0.4)"
+            - "rgba(245, 150, 40, 0.73)"
+            - "rgba(225, 40, 40, 0.59)"
+          thresholds: "1,3"
+          interval: "> 60s"
+          sparkline:
+            fillColor: "rgba(31, 118, 189, 0.18)"
+            full: false
+            lineColor: "rgb(31, 120, 193)"
+            show: false
+          valueFontSize: "50%"
+          valueMaps:
+            - op: "="
+              text: "no data"
+              value: "null"
+            - op: "="
+              text: "OKAY"
+              value: "0"
+            - op: "="
+              text: "WARN"
+              value: "1"
+            - op: "="
+              text: "UNKW"
+              value: "2"
+            - op: "="
+              text: "CRIT"
+              value: "3"
+            - op: "="
+              text: "DOWN"
+              value: "4"
+          valueName: current