Add more metrics

routingtable/mergedlocrib/metrics/mergedlocrib_metrics.go

+package metrics
+
+// MergedLocRIBMetrics represents merged local rib metrics
+type MergedLocRIBMetrics struct {
+	RIBName                     string
+	UniqueRouteCount            uint64
+	RoutesWithSingleSourceCount uint64
+}