Add education promo for App-to-Web

Adds education promo that shows where App-to-Web feature is located and
how to use it. See go/app-to-web-education for more details.

Bug: 373680430
Test: manual testing
Flag: com.android.window.flags.enable_desktop_windowing_app_to_web_education

Change-Id: I3e5f54b1f8d44ec71482d9de1c13975c663a30b8