webhook: remove resource_namespace tag in stats reporter

This addresses #3171.

As `resource_namespace` has the potential to contribute to high metrics
cardinality while not adding much value from observability perspective,
it would be ideal to disable it by default.

cmd/webhook/main.go

@@ -253,6 +253,8 @@ func main() {
 		ServiceName: serviceName,
 		Port:        webhook.PortFromEnv(8443),
 		SecretName:  secretName,
+
+		StatsReporterOptions: []webhook.StatsReporterOption{webhook.WithoutTags("resource_namespace")},
 	})
 
 	mux := http.NewServeMux()