### 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,
        state_machine_arn: Arn,
        name: Name = None,
        input: SensitiveData = None,
        trace_header: TraceHeader = None,
    ) -> StartExecutionOutput:
        state_machine: Optional[StateMachineInstance] = self.get_store(context).state_machines.get(
            state_machine_arn
        )
        if not state_machine:
            raise StateMachineDoesNotExist(f"State Machine Does Not Exist: '{state_machine_arn}'")
        # 
        state_machine_clone = copy.deepcopy(state_machine)
        if input is None:
            input_data = dict()
        else:
            try:
                input_data = json.loads(input)
            except Exception as ex:
                raise InvalidExecutionInput(str(ex))  # 
        normalised_state_machine_arn = (
            state_machine.source_arn
            if isinstance(state_machine, StateMachineVersion)
            else state_machine.arn
        )
        exec_name = name or long_uid()  #