feat: add DbLatestHeight metric to prometheus (#88)

## Description


https://forbole.atlassian.net/browse/BDU-724

## Checklist
- [x] Targeted PR against correct branch.
- [x] Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
- [ ] Wrote unit tests.  
- [x] Re-reviewed `Files changed` in the Github PR explorer.

CHANGELOG.md

@@ -1,6 +1,8 @@
 ## Unreleased
+
 ### Changes
 - ([\#74](https://github.com/forbole/juno/pull/74)) Applied `GetMissingHeights()` in `enqueueMissingBlocks()` & in `parse blocks missing` cmd
+- ([\#88](https://github.com/forbole/juno/pull/88)) Added `juno_db_latest_height` metric to prometheus monitoring
 
 ## v4.0.0
 ### Changes

logging/prometheus.go

@@ -45,6 +45,15 @@ var DbBlockCount = prometheus.NewGaugeVec(
 	[]string{"total_blocks_in_db"},
 )
 
+// DbLatestHeight represents the Telemetry counter used to track the last indexed height in the database
+var DbLatestHeight = prometheus.NewGaugeVec(
+	prometheus.GaugeOpts{
+		Name: "juno_db_latest_height",
+		Help: "Latest block height in the database.",
+	},
+	[]string{"db_latest_height"},
+)
+
 func init() {
 	err := prometheus.Register(StartHeight)
 	if err != nil {
@@ -70,4 +79,9 @@ func init() {
 	if err != nil {
 		panic(err)
 	}
+
+	err = prometheus.Register(DbLatestHeight)
+	if err != nil {
+		panic(err)
+	}
 }

parser/worker.go

@@ -358,5 +358,11 @@ func (w Worker) ExportTxs(txs []*types.Tx) error {
 	totalBlocks := w.db.GetTotalBlocks()
 	logging.DbBlockCount.WithLabelValues("total_blocks_in_db").Set(float64(totalBlocks))
 
+	dbLatestHeight, err := w.db.GetLastBlockHeight()
+	if err != nil {
+		return err
+	}
+	logging.DbLatestHeight.WithLabelValues("db_latest_height").Set(float64(dbLatestHeight))
+
 	return nil
 }