Add none option for metrics producers

Signed-off-by: Goutham <gouthamve@gmail.com>

exporters/autoexport/metrics.go

@@ -206,6 +206,9 @@ func init() {
 	RegisterMetricProducer("prometheus", func(ctx context.Context) (metric.Producer, error) {
 		return prometheusbridge.NewMetricProducer(), nil
 	})
+	RegisterMetricProducer("none", func(ctx context.Context) (metric.Producer, error) {
+		return newNoopMetricProducer(), nil
+	})
 }
 
 type readerWithServer struct {

exporters/autoexport/noop.go

@@ -7,6 +7,7 @@ import (
 	"context"
 
 	"go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 	"go.opentelemetry.io/otel/sdk/trace"
 )
 
@@ -46,3 +47,20 @@ func IsNoneMetricReader(e metric.Reader) bool {
 	_, ok := e.(noopMetricReader)
 	return ok
 }
+
+type noopMetricProducer struct{}
+
+func (e noopMetricProducer) Produce(ctx context.Context) ([]metricdata.ScopeMetrics, error) {
+	return nil, nil
+}
+
+func newNoopMetricProducer() noopMetricProducer {
+	return noopMetricProducer{}
+}
+
+// IsNoneMetricReader returns true for the exporter returned by [NewMetricReader]
+// when OTEL_METRICS_PRODUCERS environment variable is set to "none".
+func IsNoneMetricProducer(e metric.Producer) bool {
+	_, ok := e.(noopMetricProducer)
+	return ok
+}