fix: add a UUID in the task value (#1430)

The jvmName when calling from cloud function will always be 1@localhost. Add a UUID in the default task value string so we won't have multiple tasks writing to the same stream.

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Fixes #<issue_number_goes_here> ☕️

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https://github.com/GoogleCloudPlatform/java-docs-samples/blob/main/SAMPLE_FORMAT.md).

google-cloud-bigtable-stats/src/main/java/com/google/cloud/bigtable/stats/BigtableStackdriverExportUtils.java

@@ -46,6 +46,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.UUID;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import javax.annotation.Nullable;
@@ -168,7 +169,7 @@ static String getDefaultTaskValue() {
       // Generate a random number and use the same format "random_number@hostname".
       return "java-" + new SecureRandom().nextInt() + "@" + hostname;
     }
-    return "java-" + jvmName;
+    return "java-" + UUID.randomUUID() + jvmName;
   }
 
   private static MetricKind createMetricKind(Type type) {