monitoring: add prometheus monitoring

add init metrics service which uses prometheus;
add configuration for metrics service;
add monitoring metrics for blockchain,rpc,server;

pkg/core/prometheus.go

@@ -0,0 +1,76 @@
+package core
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// Metrics for monitoring service.
+var (
+	//blockHeight prometheus metric.
+	blockHeight = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Help:      "Current index of processed block",
+			Name:      "current_block_height",
+			Namespace: "neogo",
+		},
+	)
+	//persistedHeight prometheus metric.
+	persistedHeight = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Help:      "Current persisted block count",
+			Name:      "current_persisted_height",
+			Namespace: "neogo",
+		},
+	)
+	//headerHeight prometheus metric.
+	headerHeight = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Help:      "Current header height",
+			Name:      "current_header_height",
+			Namespace: "neogo",
+		},
+	)
+	//mempoolUnsortedTx prometheus metric.
+	mempoolUnsortedTx = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Help:      "Mempool Unsorted TXs",
+			Name:      "mempool_unsorted_tx",
+			Namespace: "neogo",
+		},
+	)
+	//mempoolUnverifiedTx prometheus metric.
+	mempoolUnverifiedTx = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Help:      "Mempool Unverified TXs",
+			Name:      "mempool_unverified_tx",
+			Namespace: "neogo",
+		},
+	)
+)
+
+func init() {
+	prometheus.MustRegister(
+		blockHeight,
+		persistedHeight,
+		headerHeight,
+		mempoolUnsortedTx,
+		mempoolUnverifiedTx,
+	)
+}
+
+func updatePersistedHeightMetric(pHeight uint32) {
+	persistedHeight.Set(float64(pHeight))
+}
+
+func updateHeaderHeightMetric(hHeight int) {
+	headerHeight.Set(float64(hHeight))
+}
+
+func updateBlockHeightMetric(bHeight uint32) {
+	blockHeight.Set(float64(bHeight))
+}
+
+func updateMempoolMetrics(unsortedTxnLen int, unverifiedTxnLen int) {
+	mempoolUnsortedTx.Set(float64(unsortedTxnLen))
+	mempoolUnverifiedTx.Set(float64(unverifiedTxnLen))
+}