use proxy.conf to increase code reuse

homeassistant.subdomain.conf.sample

@@ -38,9 +38,7 @@ server {
     }
     
     location /api {
-        proxy_http_version 1.1;
-        proxy_set_header Upgrade $http_upgrade;
-        proxy_set_header Connection "upgrade";
+        include /config/nginx/proxy.conf;
         set $upstream_app homeassistant;
         set $upstream_port 8123;
         set $upstream_proto http;