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/apiserver/builder/common.go

@@ -4,6 +4,7 @@ import (
 	"net/http"
 
 	grafanarest "github.com/grafana/grafana/pkg/apiserver/rest"
+	"github.com/prometheus/client_golang/prometheus"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/apimachinery/pkg/runtime/serializer"
@@ -29,6 +30,7 @@ type APIGroupBuilder interface {
 		codecs serializer.CodecFactory,
 		optsGetter generic.RESTOptionsGetter,
 		desiredMode grafanarest.DualWriterMode,
+		reg prometheus.Registerer,
 	) (*genericapiserver.APIGroupInfo, error)
 
 	// Get OpenAPI definitions

pkg/apiserver/builder/helper.go

@@ -25,6 +25,7 @@ import (
 
 	"github.com/grafana/grafana/pkg/apiserver/endpoints/filters"
 	"github.com/grafana/grafana/pkg/services/apiserver/options"
+	"github.com/prometheus/client_golang/prometheus"
 )
 
 // TODO: this is a temporary hack to make rest.Connecter work with resource level routes
@@ -128,6 +129,7 @@ func InstallAPIs(
 	optsGetter generic.RESTOptionsGetter,
 	builders []APIGroupBuilder,
 	storageOpts *options.StorageOptions,
+	reg prometheus.Registerer,
 ) error {
 	// dual writing is only enabled when the storage type is not legacy.
 	// this is needed to support setting a default RESTOptionsGetter for new APIs that don't
@@ -136,7 +138,7 @@ func InstallAPIs(
 
 	for _, b := range builders {
 		mode := b.GetDesiredDualWriterMode(dualWriteEnabled, storageOpts.DualWriterDesiredModes)
-		g, err := b.GetAPIGroupInfo(scheme, codecs, optsGetter, mode)
+		g, err := b.GetAPIGroupInfo(scheme, codecs, optsGetter, mode, reg)
 		if err != nil {
 			return err
 		}