Add logging to diagnose no-video bug (#7721)

Log in/outbound RTP stats so we can see ifn we're sending & receiving
video, and log when we successfully play the video element.

src/components/views/voip/VideoFeed.tsx

@@ -137,6 +137,7 @@ export default class VideoFeed extends React.PureComponent<IProps, IState> {
             // them with another load() which will cancel the pending one, but since we don't call
             // load() explicitly, it shouldn't be a problem. - Dave
             await element.play();
+            logger.debug((this.props.feed.isLocal ? "Local" : "Remote") + " video feed play() completed");
         } catch (e) {
             logger.info("Failed to play media element with feed", this.props.feed, e);
         }