observability: add metrics to exporter api

exporter/api/metrics.go

@@ -14,6 +14,10 @@ var (
 		Name: "ssv:exporter:stream_outbound_errors",
 		Help: "count the outbound messages failures on stream channel",
 	}, []string{"cid"})
+	metricHandleParticipantsQueryReq = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Name: "ssv:exporter:handle_participants_query_req",
+		Help: "Histogram of HTTP request durations in seconds.",
+	}, []string{"role"})
 )
 
 func reportStreamOutbound(cid string, err error) {

exporter/api/query_handlers.go

@@ -3,6 +3,7 @@ package api
 import (
 	"encoding/hex"
 	"fmt"
+	"time"
 
 	"github.com/attestantio/go-eth2-client/spec/phase0"
 	spectypes "github.com/ssvlabs/ssv-spec/types"
@@ -49,6 +50,9 @@ func HandleUnknownQuery(logger *zap.Logger, nm *NetworkMessage) {
 
 // HandleParticipantsQuery handles TypeParticipants queries.
 func HandleParticipantsQuery(logger *zap.Logger, qbftStorage *storage.QBFTStores, nm *NetworkMessage, domain spectypes.DomainType) {
+	sinceStart := time.Since(time.Now())
+	defer metricHandleParticipantsQueryReq.WithLabelValues(nm.Msg.Filter.Role).Observe(sinceStart.Seconds())
+
 	logger.Debug("handles query request",
 		zap.Uint64("from", nm.Msg.Filter.From),
 		zap.Uint64("to", nm.Msg.Filter.To),