S3 bucket name need to be unique, so added a tag for it

Author: Mazhar Islam

walkthroughs/howto-k8s-appmesh-load-test/scripts/constants.py

@@ -7,4 +7,4 @@
 PROMETHEUS_QUERY_ENDPOINT = 'http://localhost:9090/api/v1/query_range'
 
 # give your s3 bucket a unique name
-S3_BUCKET = "username-appmeshloadtester"
+S3_BUCKET = "<username-appmeshloadtester"