Refactor to use Vertex AI Notebooks rather than Colab

[benofben]

I'm a bit torn on whether this is a good idea:

Vertex AI Notebook Pro

• Probably what you use in prod
• Remains running if browser is closed

Colab Pro

• Easiest to deploy
• No notebook runtime to delete later

[benofben]

We've moved to Workbench. Fingers crossed!