docs(stepfunctions): Update Step Functions Job Poller example (#24117)

Hi team,

Updated code for Step Functions Job Poller example according to https://docs.aws.amazon.com/step-functions/latest/dg/sample-project-job-poller.html#sample-job-poller-code-example

Please check and let me know if this makes sense.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: yuyokk

packages/@aws-cdk/aws-stepfunctions/README.md

@@ -29,8 +29,8 @@ declare const getStatusLambda: lambda.Function;
 
 const submitJob = new tasks.LambdaInvoke(this, 'Submit Job', {
   lambdaFunction: submitLambda,
-  // Lambda's result is in the attribute `Payload`
-  outputPath: '$.Payload',
+  // Lambda's result is in the attribute `guid`
+  outputPath: '$.guid',
 });
 
 const waitX = new sfn.Wait(this, 'Wait X Seconds', {
@@ -42,7 +42,7 @@ const getStatus = new tasks.LambdaInvoke(this, 'Get Job Status', {
   // Pass just the field named "guid" into the Lambda, put the
   // Lambda's result in a field called "status" in the response
   inputPath: '$.guid',
-  outputPath: '$.Payload',
+  outputPath: '$.status',
 });
 
 const jobFailed = new sfn.Fail(this, 'Job Failed', {