Expose guzzle proxy options for the license check

[rbridge]

For my current working environment the only way for our sites to contact services outside our network is for that traffic to be routed through a proxy. When attempting to set up Nova in my staging environment I found that it couldn't reach the license check endpoint.

Would it be possible to add a config option for http and https proxies as part of the nova config? I saw that it was just using the standard Laravel HTTP Client, so ideally I could just inject the proxy Guzzle Options.