Fix #49 large zip scenario file upload failure

When user uploads a large zip file for scenario file, the console generates an error message.

"Error ETagMissing: No access to ETag property on response. Check CORS configuration to expose ETag header."

Adding "ETag" header to ExposeHeaders will fix the error.
I references https://docs.amplify.aws/lib/storage/getting-started/q/platform/js#amazon-s3-bucket-cors-policy-setup and aws-amplify/amplify-cli#297 for solutions.

Author: naxxster

deployment/distributed-load-testing-on-aws.yaml

@@ -633,6 +633,8 @@ Resources:
               - !Sub https://${ConsoleCloudFront.DomainName}
             AllowedHeaders:
               - '*'
+            ExposedHeaders:
+              - 'ETag'
       Tags:
         - Key: SolutionId
           Value: SO0062