Add information about the participant's platform

[cactyx]

This would be really useful to handle the different behaviour of various platforms when users use controls.

XBOX for example doesn't feature an option to hold a button. Over on YouPlay that causes people to be unable to walk correctly, instead they just move two pixels and have to spam buttons if they want to walk further distances.

In this case this piece of information would allow me to press that direction button with an active delay, in case the viewer is using an XBOX.

This could be achieved by passing on either the User Agent or a Platform enum value like xbox, web, mobile.

I'm just not sure if that could be something that would cause problems with some privacy policy.