Bring back websocket tests

I wasn't able to figure out how to update the websocket test after making some changes and updating to OTP 25. The websocket test was removed in: https://github.com/Main-Proxy/main_proxy/pull/20/commits/6b50bf3282ceace3e79c337504a1a20979b99973

And I created https://github.com/Main-Proxy/main_proxy/pull/21 to make it easier to restore them.