export config file hash in a metric (#3768)

Signed-off-by: zounengren <zounengren@cmss.chinamobile.com>

plugin/reload/metrics.go

@@ -14,4 +14,11 @@ var (
 		Name:      "failed_count_total",
 		Help:      "Counter of the number of failed reload attempts.",
 	})
+
+	reloadInfo = prometheus.NewGaugeVec(prometheus.GaugeOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: "reload",
+		Name:      "version_info",
+		Help:      "A metric with a constant '1' value labeled by hash, and value which type of hash generated.",
+	}, []string{"hash", "value"})
 )