Added gauge libsonnet (#162)

* Added gauge libsonnet

grafonnet/gauge.libsonnet

@@ -0,0 +1,32 @@
+{
+  new(
+    title,
+    datasource=null,
+    calc='mean',
+    description='',
+    height=null,
+    transparent=null,
+  )::
+    {
+      [if description != '' then 'description']: description,
+      [if height != null then 'height']: height,
+      [if transparent != null then 'transparent']: transparent,
+      title: title,
+      type: 'gauge',
+      datasource: datasource,
+      options: {
+        fieldOptions: {
+          calcs: [
+            calc,
+          ],
+        },
+      },
+      _nextTarget:: 0,
+      addTarget(target):: self {
+        local nextTarget = super._nextTarget,
+        _nextTarget: nextTarget + 1,
+        targets+: [target { refId: std.char(std.codepoint('A') + nextTarget) }],
+      },
+    },
+
+}

grafonnet/grafana.libsonnet

@@ -18,4 +18,5 @@
   cloudwatch:: import 'cloudwatch.libsonnet',
   elasticsearch:: import 'elasticsearch.libsonnet',
   heatmapPanel:: import 'heatmap_panel.libsonnet',
+  gauge:: import 'gauge.libsonnet',
 }