Fix for parent-child state machine calls

[nplusterio]

Description

• Fix for error when executing a child state machine from parent state machine as a task

Dependencies

• Fix for parent-child state machine calls stepfunctions-localhost#14

Steps to replicate issue:

1. Given the following simple serverless.yml example:

service: my-step-functions-local

provider:
  name: aws
  runtime: nodejs18.x
  region: us-east-2

custom:
  application: MyStepFunctions

  stepFunctionsLocal:
    accountId: 101010101010
    region: us-east-2

stepFunctions:
  stateMachines:
    childStateMachine:
      name: child-state-machine
      definition:
        Comment: "Child State Machine"
        StartAt: SayHello
        States:
          SayHello:
            Type: Pass
            Result: "Hello from Child State Machine"
            End: true
    parentStateMachine:
      name: parent-state-machine
      definition:
        Comment: "Parent State Machine"
        StartAt: ExecuteChildStateMachine
        States:
          ExecuteChildStateMachine:
            Type: Task
            Resource: "arn:aws:states:::states:startExecution.sync:2"
            Parameters:
              StateMachineArn: "arn:aws:states:us-east-2:101010101010:stateMachine:child-state-machine"
            TimeoutSeconds: 599
            End: true

plugins:
  - serverless-step-functions
  - serverless-step-functions-local
  - serverless-offline

2. Run sls offline start
3. Execute Child State Machine directly by running aws stepfunctions --endpoint-url http://localhost:8083 start-execution --state-machine-arn arn:aws:states:us-east-2:101010101010:stateMachine:child-state-machine (working ✅)
4. Execute Parent State Machine (which executes the child state machine as a task) by running aws stepfunctions --endpoint-url http://localhost:8083 start-execution --state-machine-arn arn:aws:states:us-east-2:101010101010:stateMachine:parent-state-machine (not working ❌). Getting this error message:

   arn:aws:states:us-east-2:101010101010:execution:parent-state-machine:bbbdc711-2462-4dcc-b6d9-f242c84dbd2c : {"Type":"TaskFailed","PreviousEventId":4,"TaskFailedEventDetails":{"ResourceType":"states","Resource":"startExecution.sync:2","Error":"StepFunctions-AWSStepFunctionsException","Cause":"The security token included in the request is invalid. (Service: AWSStepFunctions; Status Code: 400; Error Code: UnrecognizedClientException; Request ID: 338d459f-04e2-4f57-89cc-8d9b9364cfa8; Proxy: null)"}}
   

This PR along with the Dependency PR mentioned above should solve this issue.