Use dedicated thread for Metrics PeriodicReader

examples/metrics-basic/src/main.rs

@@ -11,7 +11,7 @@ fn init_meter_provider() -> opentelemetry_sdk::metrics::SdkMeterProvider {
         //  .with_encoder(|writer, data|
         //    Ok(serde_json::to_writer_pretty(writer, &data).unwrap()))
         .build();
-    let reader = PeriodicReader::builder(exporter, runtime::Tokio).build();
+    let reader = PeriodicReader::builder(exporter).build();
     let provider = SdkMeterProvider::builder()
         .with_reader(reader)
         .with_resource(Resource::new([KeyValue::new(