related-applications sample documentation needs update for ML-based installs

Chrome has released an ML-based gate for app install banners on Android.

https://developer.chrome.com/blog/how_chrome_helps_users_install_the_apps_they_value

The demo instructions for the samples under app-install-banner/, including related-application/, need to be updated with instructions on how developers can test these flows using the sample code.

It appears that the previous flag, `chrome://flags#bypass-app-banner-engagement-checks`, will no longer work as of M131.

Tagging @dmurph as they are familiar with these APIs