fix(docker): use a tunable for fastapi proxy host value

On aur-dev.archlinux.org, we use a proxy tunnel through our
internal nginx. This allows us to rewrite the Host header
based on whatever port we wish within internal nginx config.

Signed-off-by: Kevin Morris <kevr@0cost.org>

docker-compose.aur-dev.yml

@@ -69,6 +69,8 @@ services:
       - data:/data
 
   nginx:
+    environment:
+      - NGINX_PROXY_PORT=443
     restart: always
     volumes:
       - data:/data