### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

Currently, when passing `$$.Execution.StartTime` as a parameter to a SFN lambda, it is coming in in the format `HH:MM:SS.###`.

### Expected Behavior

`$$.Execution.StartTime` should be an ISO 8601 datetime string.

### How are you starting LocalStack?

With a docker-compose file

### Steps To Reproduce

This is run in a docker compose file.

Step function definition is

```json
{
  "Comment": "Sample SFN",
  "StartAt": "SampleLambda",
  "States": {    
    "SampleLambda": {
      "Type": "Task",
      "Resource": "arn:aws:states:::lambda:invoke",
      "End": true,
      "Parameters": {
        "FunctionName": "Sample-Function",
        "Payload": {
          "data": {
            "startDateTime.$": "$$.Execution.StartTime"
          }
        }
      }
    }
  }
}
```

### Environment

```markdown
- OS: Mac OS Ventura 13.6.1
- LocalStack:
LocalStack version: 3.0.1.dev
LocalStack build date: 2023-11-20
LocalStack build git hash: 3e32b438
```


### Anything else?

Thank you so much for your hard work.
self, context: RequestContext, execution_arn: Arn
    ) -> DescribeExecutionOutput:
        execution: Execution = self._get_execution(context=context, execution_arn=execution_arn)
        return execution.to_describe_output()
    def list_executions(
        self,
        context: RequestContext,
        state_machine_arn: Arn = None,
        status_filter: ExecutionStatus = None,
        max_results: PageSize = None,
        next_token: ListExecutionsPageToken = None,
        map_run_arn: LongArn = None,
        redrive_filter: ExecutionRedriveFilter = None,
    ) -> ListExecutionsOutput:
        # 
        executions: ExecutionList = [
            execution.to_execution_list_item()
            for execution in self.get_store(context).executions.values()
            if execution.state_machine.arn == state_machine_arn
        ]
        return ListExecutionsOutput(executions=executions)
    def list_state_machines(
        self, context: RequestContext, max_results: PageSize = None, next_token: PageToken = None
    ) -> ListStateMachinesOutput:
        # 
        state_machines: StateMachineList = [