feat: add proper openresty support

This change allows supporting the openresty package as installed on Ubuntu 18.04 from the official openresty package repository, while also returning general nginx support.

Closes #3675

docker/usr/local/openresty/nginx/conf/nginx.conf

@@ -0,0 +1,30 @@
+user www-data;
+worker_processes auto;
+pid /run/openresty.pid;
+include /usr/local/openresty/nginx/conf/modules-enabled/*.conf;
+
+events {
+  worker_connections 768;
+}
+
+http {
+  sendfile on;
+  tcp_nopush on;
+  tcp_nodelay on;
+  keepalive_timeout 65;
+  types_hash_max_size 2048;
+
+  include /usr/local/openresty/nginx/conf/mime.types;
+  default_type application/octet-stream;
+
+  ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
+  ssl_prefer_server_ciphers on;
+
+  access_log /var/log/openresty/access.log;
+  error_log /var/log/openresty/error.log;
+
+  gzip on;
+
+  include /usr/local/openresty/nginx/conf/conf.d/*.conf;
+  include /usr/local/openresty/nginx/conf/sites-enabled/*;
+}