fix: add go-eth metrics flags (#4269)

cmd/harmony/flags.go

@@ -233,6 +233,11 @@ var (
 		cacheTimeFlag,
 		cacheSizeFlag,
 	}
+
+	metricsFlags = []cli.Flag{
+		metricsETHFlag,
+		metricsExpensiveETHFlag,
+	}
 )
 
 var (
@@ -339,6 +344,7 @@ func getRootFlags() []cli.Flag {
 	flags = append(flags, prometheusFlags...)
 	flags = append(flags, syncFlags...)
 	flags = append(flags, shardDataFlags...)
+	flags = append(flags, metricsFlags...)
 
 	return flags
 }
@@ -1754,6 +1760,22 @@ var (
 	}
 )
 
+// metrics flags required for the go-eth library
+// https://github.com/ethereum/go-ethereum/blob/master/metrics/metrics.go#L35-L55
+var (
+	metricsETHFlag = cli.BoolFlag{
+		Name:     "metrics", // https://github.com/ethereum/go-ethereum/blob/master/metrics/metrics.go#L30
+		Usage:    "flag required to enable the eth metrics",
+		DefValue: false,
+	}
+
+	metricsExpensiveETHFlag = cli.BoolFlag{
+		Name:     "metrics.expensive", // https://github.com/ethereum/go-ethereum/blob/master/metrics/metrics.go#L33
+		Usage:    "flag required to enable the expensive eth metrics",
+		DefValue: false,
+	}
+)
+
 func applyShardDataFlags(cmd *cobra.Command, cfg *harmonyconfig.HarmonyConfig) {
 	if cli.IsFlagChanged(cmd, enableShardDataFlag) {
 		cfg.ShardData.EnableShardData = cli.GetBoolFlagValue(cmd, enableShardDataFlag)