Init dualwriter metrics (#89003)

* Pass prometheus registerer to the dual writer

* Fix tests

* Remove unused var

* Fix tests

* Uncomment test

* Remove leading line

* Fix tests. Reuse registerer if there's already one

* Lint

* Improve double registering logic

* Rebase main

pkg/registry/apis/dashboardsnapshot/register.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"github.com/gorilla/mux"
+	"github.com/prometheus/client_golang/prometheus"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
@@ -71,6 +72,7 @@ func RegisterAPIService(
 	cfg *setting.Cfg,
 	features featuremgmt.FeatureToggles,
 	sql db.DB,
+	reg prometheus.Registerer,
 ) *SnapshotsAPIBuilder {
 	if !features.IsEnabledGlobally(featuremgmt.FlagGrafanaAPIServerWithExperimentalAPIs) {
 		return nil // skip registration unless opting into experimental apis
@@ -129,6 +131,7 @@ func (b *SnapshotsAPIBuilder) GetAPIGroupInfo(
 	codecs serializer.CodecFactory, // pointer?
 	optsGetter generic.RESTOptionsGetter,
 	_ grafanarest.DualWriterMode,
+	_ prometheus.Registerer,
 ) (*genericapiserver.APIGroupInfo, error) {
 	apiGroupInfo := genericapiserver.NewDefaultAPIGroupInfo(dashboardsnapshot.GROUP, scheme, metav1.ParameterCodec, codecs)
 	storage := map[string]rest.Storage{}