fix(proxy): raise nginx worker rlimit above worker_connections

nginx inherited systemd's soft LimitNOFILE of 1024, so every start logged
"2048 worker_connections exceed open file resource limit: 1024" and the
worker_connections value could not actually be reached.

Set worker_rlimit_nofile to 65536. Bounded from above by a systemd drop-in
at /etc/systemd/system/nginx.service.d/override.conf (LimitNOFILE=65536),
since the master's hard limit caps what workers may request.

deployment/proxy/nginx.conf

@@ -12,6 +12,11 @@
 
 user www-data;
 worker_processes auto;
+# Raise the file-descriptor rlimit for the workers. Must stay <= the master's
+# RLIMIT_NOFILE *hard* limit, otherwise nginx refuses to start with
+# "setrlimit(RLIMIT_NOFILE) failed". Bounded from above by the systemd drop-in
+# /etc/systemd/system/nginx.service.d/override.conf (LimitNOFILE=65536).
+worker_rlimit_nofile 65536;
 pid /run/nginx.pid;
 
 error_log /var/log/nginx/error.log warn;