Proxy support

**Is your feature request related to a problem? Please describe.** I want to use Nyxt to browse the I2P network (an overlay network similar to Tor). Unfortunately to do so an http proxy is required, which I believe is currently not supported by Nyxt. Apologies if such a feature (or some way to accomplish proxying, perhaps through some advanced configuration) already exists in Nyxt. I am a newcomer to Nyxt and to Common Lisp in general. I also want to say that this is an incredible browser.