[feature] websocket support

[onichandame]

I would like to use goose to test websocket endpoints. It seems that the controller already has websocket built-in, so I guess it won't be implausible to integrate ws into the GooseUser?

[jeremyandrews]

Patches are welcome. Eventually the goal is to make the GooseClient more generic to allow many other types of clients, but right now you're likely to run into a lot of assumptions around Reqwest.