[functional testing] Add VNC server to functional test runner container

[msheiny]

Description

It is very difficult currently to debug why functional tests fail using the new tor browser selenium logic. The upstream selenium team offers docker containers packed with firefox/chrome that include a VNC server for visual view of what the browser is doing. This would be insanely useful for us during development.

User Research Evidence

Doesn't affect end-users, only developers.

User Stories

As a developer, it would aid in my troubleshooting to be able to visually see the Tor Browser tests running while they are running.

Epic: #3659

[redshiftzero]

resolved by #3817