### 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.
def __init__(self, execution: Execution):
        self.execution: Execution = execution
    def terminated(self) -> None:
        exit_program_state: ProgramState = self.execution.exec_worker.env.program_state()
        self.execution.stop_date = datetime.datetime.now()
        if isinstance(exit_program_state, ProgramEnded):
            self.execution.exec_status = ExecutionStatus.SUCCEEDED
            self.execution.output = to_json_str(
                self.execution.exec_worker.env.inp, separators=(",", ":")
            )
        elif isinstance(exit_program_state, ProgramStopped):
            self.execution.exec_status = ExecutionStatus.ABORTED
        elif isinstance(exit_program_state, ProgramError):
            self.execution.exec_status = ExecutionStatus.FAILED
            self.execution.error = exit_program_state.error["error"]
            self.execution.cause = exit_program_state.error["cause"]
        elif isinstance(exit_program_state, ProgramTimedOut):
            self.execution.exec_status = ExecutionStatus.TIMED_OUT
        else:
            raise RuntimeWarning(
                f"Execution ended with unsupported ProgramState type '{type(exit_program_state)}'."
            )
        self.execution._publish_execution_status_change_event()
class Execution: