feat(go): expose gateway async sink metrics

go/vehicle-gateway/cmd/gateway/main_test.go

@@ -56,6 +56,23 @@ func TestGatewayDefaultsTo100KConnectionCeiling(t *testing.T) {
 	}
 }
 
+func TestGatewayPassesMetricsRegistryToAsyncSink(t *testing.T) {
+	source, err := os.ReadFile("main.go")
+	if err != nil {
+		t.Fatalf("read main.go: %v", err)
+	}
+	for _, want := range []string{
+		"buildSink(ctx, logger, registry)",
+		"Metrics:          registry",
+		`Name:             "nats"`,
+		`Name:             "kafka"`,
+	} {
+		if !strings.Contains(string(source), want) {
+			t.Fatalf("gateway async sink metrics wiring missing %s", want)
+		}
+	}
+}
+
 func TestNATSSinkConfigFromEnvDefaultsToGoSubjects(t *testing.T) {
 	t.Setenv("NATS_URL", "nats://172.17.111.56:4222")