Run pack updating on its own thread #23
Description
Currently pack updates will block: the main thread at startup, the main thread when running a command, the netty worker thread when receiving the webhook.
The first one makes sense, players shouldn't be allowed to join before there's a valid resourcepack available for them. The other two are problems though. Running the command will freeze the server until it's finished (especially noticeable when there's a slow connection between the server and git host and it has to download the repo). The webhook runs on the netty thread probably aren't a big problem? Not sure, best to start the new thread in that case too.