metrics: add server interceptor missing prometheus collector wrapped method

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

interceptors/metrics/interceptors.go

@@ -2,6 +2,7 @@ package metrics
 
 import (
 	grpc_prometheus "github.com/grpc-ecosystem/go-grpc-prometheus"
+	"github.com/prometheus/client_golang/prometheus"
 	"google.golang.org/grpc"
 
 	"go.linka.cloud/grpc/interceptors"
@@ -13,13 +14,14 @@ type Registerer interface {
 }
 
 type Interceptors interface {
-	interceptors.Interceptors
-	Registerer
+	ServerInterceptors
+	ClientInterceptors
 }
 
 type ServerInterceptors interface {
-	interceptors.ServerInterceptors
 	Registerer
+	interceptors.ServerInterceptors
+	prometheus.Collector
 }
 
 type ClientInterceptors interface {
@@ -31,6 +33,18 @@ type metrics struct {
 	c *grpc_prometheus.ClientMetrics
 }
 
+func (m *metrics) Describe(descs chan<- *prometheus.Desc) {
+	if m.s != nil {
+		m.s.Describe(descs)
+	}
+}
+
+func (m *metrics) Collect(c chan<- prometheus.Metric) {
+	if m.s != nil {
+		m.s.Collect(c)
+	}
+}
+
 func (m *metrics) Register(svc service.Service) {
 	if m.s != nil {
 		m.s.InitializeMetrics(svc)