Use an HTTP proxy for resolving the admin address dynamically

nginx/config.py

@@ -2,15 +2,11 @@
 
 import jinja2
 import os
-import socket
 	
 convert = lambda src, dst, args: open(dst, "w").write(jinja2.Template(open(src).read()).render(**args))
 
 args = os.environ.copy()
 
-if "ADMIN_ADDRESS" not in os.environ:
-    args["ADMIN_ADDRESS"] = socket.gethostbyname("admin")
-
 args["TLS"] = {
     "cert": ("/certs/cert.pem", "/certs/key.pem"),
     "letsencrypt": ("/certs/letsencrypt/live/mailu/fullchain.pem",