fix: shutdown built in metrics meter provider

Author: surbhigarg92

google-cloud-spanner/src/main/java/com/google/cloud/spanner/BuiltInOpenTelemetryMetricsProvider.java

@@ -42,6 +42,7 @@
 import java.util.HashMap;
 import java.util.Map;
 import java.util.UUID;
+import java.util.concurrent.TimeUnit;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import javax.annotation.Nullable;
@@ -65,8 +66,14 @@ OpenTelemetry getOrCreateOpenTelemetry(String projectId, @Nullable Credentials c
         SdkMeterProviderBuilder sdkMeterProviderBuilder = SdkMeterProvider.builder();
         BuiltInOpenTelemetryMetricsView.registerBuiltinMetrics(
             SpannerCloudMonitoringExporter.create(projectId, credentials), sdkMeterProviderBuilder);
-        this.openTelemetry =
-            OpenTelemetrySdk.builder().setMeterProvider(sdkMeterProviderBuilder.build()).build();
+        SdkMeterProvider sdkMeterProvider = sdkMeterProviderBuilder.build();
+        this.openTelemetry = OpenTelemetrySdk.builder().setMeterProvider(sdkMeterProvider).build();
+        Runtime.getRuntime()
+            .addShutdownHook(
+                new Thread(
+                    () -> {
+                      sdkMeterProvider.shutdown().join(5, TimeUnit.SECONDS);
+                    }));
       }
       return this.openTelemetry;
     } catch (IOException ex) {