Improves GitHub Actions workflow

[aendra-rininsland]

I used an earlier version of Starter for a project recently and noticed the CI wasn't working as expected. From this I realised that it's not actually building the code in CI or installing dependencies.

This PR improves the GitHub Actions workflow by:

• Moving built/ code to .gitignore
• built/ removed from VC
• npm run build run via postinstall hook
• actions/setup-node added to workflow so code is built in CI