Create Devcontainer (Codespace)

Create a dev container for the app. The configuration should allow you to run, build, test and develop the app as you would locally. Require certain extensions? Install them. 

[Docs here](https://docs.github.com/en/codespaces/setting-up-your-project-for-codespaces/adding-a-dev-container-configuration/introduction-to-dev-containers)
