### 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.
Source="aws.states",
            Resources=[self.exec_arn],
            DetailType="Step Functions Execution Status Change",
            Detail=to_json_str(
                
                DescribeExecutionOutput(
                    executionArn=self.exec_arn,
                    stateMachineArn=self.state_machine.arn,
                    stateMachineAliasArn=None,
                    stateMachineVersionArn=None,
                    name=self.name,
                    status=self.exec_status,
                    startDate=self.start_date,
                    stopDate=self.stop_date,
                    input=input_value,
                    inputDetails=self.input_details,
                    output=output_value,
                    outputDetails=output_details,
                    error=self.error,
                    cause=self.cause,
                )
            ),
        )
        try:
            self._get_events_client().put_events(Entries=[entry])
        except Exception:
            LOG.exception(
                f"Unable to send notification of Entry='{entry}' for Step Function execution with Arn='{self.exec_arn}' to EventBridge."
            )