feat: listen to a unix socket instead of tcp

[goeo-]

caddy v2 seems to have this as a fucked up bind syntax: bind unix//run/caddy

would be cool to have for, for example, use with cloudflared, but seems like it'll require a bunch of changes

[Lemmmy]

Should hopefully only need to change the bind directive parser and the listener creation in httpserver/server.go#Listen()