[feature]: Add VsCode JsonSchema for stacked.json

[Pebkac03]

Is your feature request related to a problem? Please describe.

Recently when experimenting with macros for another project I learned about VsCode JSON-schemas and the ability to add custom ones. Just out of curiosity I checked if my stacked project had one for stacked.json and realised it didn't.

Describe the solution you would like

Including a JSON-schema in .vscode for project created using stacked create app <appname>.

Additional Context

I'd love input on this regarding requirements, usefullness, implementation, and other features to add to the scope (relevant CLI flags, same feature for Android Studio, etc). If we want to add it I'd be happy to do it and create a PR.