scripts/metricsgen: add the initial version of metricsgen

scripts/metricsgen/testdata/basic/metrics.go

@@ -0,0 +1,9 @@
+package basic
+
+import "github.com/go-kit/kit/metrics"
+
+// Metrics contains metrics exposed by this package.
+type Metrics struct {
+	// simple metric that tracks the height of the chain.
+	Height metrics.Gauge
+}