Specify web proxy in SignalR connection building
Specify web proxy in SignalR connection building

Might solve https://github.com/ppy/osu/discussions/17897 (depends on how
adeptly signalr falls back to long polling if/when is fails to websocket
via the proxy, or maybe succeed).

As with the framework side change, I've tested this to not break a
zero-proxy flow. Intending to have the user test this after next
release.

Reference:
https://stackoverflow.com/questions/59343807/get-system-default-web-proxy-in-net-core
/
https://stackoverflow.com/questions/13515058/using-signalr-client-through-a-web-proxy

ppy/osu,ppy/osu,peppy/osu,NeoAdonis/osu,peppy/osu,ppy/osu,peppy/osu,NeoAdonis/osu,NeoAdonis/osu