Support for multi domain TWA

**Is your feature request related to a problem? Please describe.**
Sometimes developers use different domains for different parts of their application. A developer could use login.example.com when users are logging in into their service or checkout.example.com in their shopping cart experience.

When using Trusted Web Activities, developers want to maintain the user in full screen when navigating across those domains.

**Describe the solution you'd like**
Allow developers to specify additional trusted origins (in twa-manifest.json?).

See: https://github.com/GoogleChrome/android-browser-helper/tree/master/demos/twa-multi-domain