Support proxies

[jsoref]

I'd like to be able to use GraphiQL on a computer that requires a proxy to connect to the internet (w/o relying on system settings).

https://electronjs.org/docs/api/session#sessetproxyconfig-callback

[igitur]

It seems that the system proxy settings are ignored too, right?

[jsoref]

I can't remember. We're specifically using a (ssh-socks) proxy for testing, we only want traffic that GraphiQL is sending to be sent to the proxy, not all traffic, so whether or not it could support the system proxy settings is irrelevant to our use case.