### 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,
        name: Name,
        arn: Arn,
        definition: Definition,
        role_arn: Arn,
        create_date: Optional[datetime] = None,
        sm_type: Optional[StateMachineType] = None,
        logging_config: Optional[LoggingConfiguration] = None,
        tags: Optional[TagList] = None,
        tracing_config: Optional[TracingConfiguration] = None,
    ):
        self.name = name
        self.arn = arn
        self.revision_id = None
        self.definition = definition
        self.role_arn = role_arn
        self.create_date = create_date or datetime.now()
        self.sm_type = sm_type or StateMachineType.STANDARD
        self.logging_config = logging_config
        self.tags = tags
        self.tracing_config = tracing_config
    def describe(self) -> DescribeStateMachineOutput: