Add traffic to existing style example

[cammace]

Currently we only have a style which includes the traffic tileset. We should create an example which shows how to make use of this tileset to display traffic on a users custom style using runtime. Note that this example should wait till mapbox/mapbox-gl-native#7285 is resolved so we show to proper way of how to do this.

[zugaldia]

We should use the upcoming traffic plugin in https://github.com/mapbox/mapbox-plugins-android for this example.