fix: use metadata informer for agent controller

The Prometheus agent controller didn't use the metadata informer for
secrets and configmaps as implemented in #5424 and #5448 for the other
controllers.

Signed-off-by: Simon Pasquier <spasquie@redhat.com>

pkg/prometheus/agent/operator.go

@@ -32,6 +32,7 @@ import (
 	"k8s.io/apimachinery/pkg/labels"
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/metadata"
 	"k8s.io/client-go/rest"
 	"k8s.io/client-go/tools/cache"
 	"k8s.io/utils/ptr"
@@ -56,7 +57,9 @@ const (
 // monitoring configurations.
 type Operator struct {
 	kclient  kubernetes.Interface
+	mdClient metadata.Interface
 	mclient  monitoringclient.Interface
+
 	logger   log.Logger
 	accessor *operator.Accessor
 
@@ -92,6 +95,11 @@ func New(ctx context.Context, restConfig *rest.Config, conf operator.Config, log
 		return nil, fmt.Errorf("instantiating kubernetes client failed: %w", err)
 	}
 
+	mdClient, err := metadata.NewForConfig(restConfig)
+	if err != nil {
+		return nil, fmt.Errorf("instantiating metadata client failed: %w", err)
+	}
+
 	mclient, err := monitoringclient.NewForConfig(restConfig)
 	if err != nil {
 		return nil, fmt.Errorf("instantiating monitoring client failed: %w", err)
@@ -111,6 +119,7 @@ func New(ctx context.Context, restConfig *rest.Config, conf operator.Config, log
 
 	c := &Operator{
 		kclient:               client,
+		mdClient:              mdClient,
 		mclient:               mclient,
 		logger:                logger,
 		config:                conf,
@@ -213,10 +222,10 @@ func New(ctx context.Context, restConfig *rest.Config, conf operator.Config, log
 	}
 
 	c.cmapInfs, err = informers.NewInformersForResource(
-		informers.NewKubeInformerFactories(
+		informers.NewMetadataInformerFactory(
 			c.config.Namespaces.PrometheusAllowList,
 			c.config.Namespaces.DenyList,
-			c.kclient,
+			c.mdClient,
 			resyncPeriod,
 			func(options *metav1.ListOptions) {
 				options.LabelSelector = prompkg.LabelPrometheusName
@@ -229,10 +238,10 @@ func New(ctx context.Context, restConfig *rest.Config, conf operator.Config, log
 	}
 
 	c.secrInfs, err = informers.NewInformersForResource(
-		informers.NewKubeInformerFactories(
+		informers.NewMetadataInformerFactory(
 			c.config.Namespaces.PrometheusAllowList,
 			c.config.Namespaces.DenyList,
-			c.kclient,
+			c.mdClient,
 			resyncPeriod,
 			func(options *metav1.ListOptions) {
 				options.FieldSelector = secretListWatchSelector.String()