Playwright test suite in CI

* Add github actions CI script 
* implement "infinite scroll" content web server with necessary endpoints (load, unload etc)
* Add playwright test suite that tests basic library properties (content is loaded only when inside the viewport and unloaded otherwise)

Take inspiration from https://wanago.io/2024/04/29/react-infinite-scrolling-e2e-playwright/ for end-to-end web testing with playwright