JupyterHub Integration into Unity Marketplace: Create Marketplace JSON

[galenatjpl]

Create the Unity Marketplace JSON file, and directory structure under here:
https://github.com/unity-sds/unity-marketplace/tree/main/applications

See also documentation here:
https://unity-sds.gitbook.io/docs/developer-docs/common-services/docs/users-guide/deployment/deployment-concepts-and-infrastructure/unity-marketplace