[#373] metrics: Move labels to consts

To unify label naming all lable keys and other consts are moved to
one file.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/metrics/innerring.go

@@ -8,13 +8,6 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 )
 
-const (
-	innerRingSubsystem    = "ir"
-	innerRingLabelSuccess = "success"
-	innerRingLabelType    = "type"
-	innerRingNamespace    = "frostfs_ir"
-)
-
 // InnerRingServiceMetrics contains metrics collected by inner ring.
 type InnerRingServiceMetrics struct {
 	epoch             prometheus.Gauge
@@ -43,7 +36,7 @@ func NewInnerRingMetrics() *InnerRingServiceMetrics {
 			Subsystem: innerRingSubsystem,
 			Name:      "event_duration_seconds",
 			Help:      "Duration of processing of inner-ring events",
-		}, []string{innerRingLabelType, innerRingLabelSuccess})
+		}, []string{typeLabel, successLabel})
 	)
 
 	return &InnerRingServiceMetrics{
@@ -66,8 +59,8 @@ func (m *InnerRingServiceMetrics) SetHealth(s int32) {
 
 func (m *InnerRingServiceMetrics) AddEvent(d time.Duration, typ string, success bool) {
 	m.eventDuration.With(prometheus.Labels{
-		innerRingLabelType:    typ,
-		innerRingLabelSuccess: strconv.FormatBool(success),
+		typeLabel:    typ,
+		successLabel: strconv.FormatBool(success),
 	}).Observe(d.Seconds())
 }