Automatically publish package updates

I'm doing this manually at the moment for `@gonzo-engineering/dummy-ui` and `@gonzo-engineering/libs`, would be nicer and probably safer to do it more methodically.

https://dev.to/ugglr/publish-update-npm-packages-with-github-actions-1m8l

https://github.com/marketplace/actions/publish-to-npm

https://github.com/JS-DevTools/npm-publish