Adds a protocol handler for notebook open, which can be used from browsers
Uses extension-based handler support so all URIs must start with `azuredatastudio://microsoft.notebook`
Adds 2 actions:
- `/new` opens a new empty notebook
- `/open` opens a HTTP/S file as an untitled notebook or text document
Sample URL:
```
azuredatastudio://microsoft.notebook/open?url=https%3A%2F%2Fraw.githubusercontent.com%2Fkevcunnane%2Fmsbuild_ads_demo%2Fmaster%2F0_YoAzdata.ipynb
```