### 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.
import os
from typing import Final
from tests.aws.services.stepfunctions.templates.template_loader import TemplateLoader
_THIS_FOLDER: Final[str] = os.path.dirname(os.path.realpath(__file__))
class BaseTemplate(TemplateLoader):
    BASE_INVALID_DER: Final[str] = os.path.join(_THIS_FOLDER, "statemachines/invalid_der.json5")
    BASE_PASS_RESULT: Final[str] = os.path.join(_THIS_FOLDER, "statemachines/pass_result.json5")
    BASE_TASK_SEQ_2: Final[str] = os.path.join(_THIS_FOLDER, "statemachines/task_seq_2.json5")
    BASE_WAIT_1_MIN: Final[str] = os.path.join(_THIS_FOLDER, "statemachines/wait_1_min.json5")
    BASE_RAISE_FAILURE: Final[str] = os.path.join(_THIS_FOLDER, "statemachines/raise_failure.json5")
    RAISE_EMPTY_FAILURE: Final[str] = os.path.join(
        _THIS_FOLDER, "statemachines/raise_empty_failure.json5"
    )
    WAIT_AND_FAIL: Final[str] = os.path.join(_THIS_FOLDER, "statemachines/wait_and_fail.json5")
    QUERY_CONTEXT_OBJECT_VALUES: Final[str] = os.path.join(
        _THIS_FOLDER, "statemachines/query_context_object_values.json5"
    )