Drop gorilla/mux in favour of http.ServeMux
Description
It recently came to our attention that the gorilla/mux package we're using is quite out of date. A community contribution has kindly upgraded this, however, I noticed upon review that we're using gorilla/mux almost entirely to perform one path match for /proxy and use no additional feature.
Go's own http library is probably capable enough to do everything we need without this dependency.
Proposal
Drop gorilla/mux and implement the same variable parsing rules for the /proxy path.
gorilla/websocket will of course continue to be used to handle websocket functionality.
Links to related issues and merge requests / references
Edited by Arran Walker