Build error for genai-prompt-chaining-hitl usecase

Hello, thank you for your work on these examples!

I'm trying to deploy the [genai-prompt-chaining-hitl](https://github.com/aws-samples/aws-stepfunctions-examples/tree/main/usecases/genai-prompt-chaining-hitl) usecase to one of my AWS accounts. When I follow the steps in the README, I get the following error:

```bash
➜ cdk (main) ✔ cdk deploy --all
Traceback (most recent call last):
File "/...path-to-clone.../aws-stepfunctions-examples/usecases/genai-prompt-chaining-hitl/stack/cdk/app.py", line 5, in
import aws_cdk as cdk
ModuleNotFoundError: No module named 'aws_cdk'

Subprocess exited with error 1
```

It it possible I need to install/manage some prerequisite libraries before being able to deploy? If so, could you specify which ones and how I can best set them up? Thanks!