Duplicate Google Duo app caller video preview feature

Issue generated from Tuleap's migration script. Originally submitted by: Dennis McKernan (dennismckernan)

Duplicate Google Duo app caller video preview feature.

The new Google Duo app has the 'Knock Knock' feature to show a video preview of the caller to 'introduce' the call:

The video preview feautre allows the recipient to make a more comfortable decision to accept the call by seeing the calling party before answering.

Thanks much for all your hard work on this fantastic FOSS project! The automatic updates are working seamlessly as well.