add include for `root_top.conf` in the nginx.conf

Allow custom configuration of the root config in the top of the file. This can be used to load modules, which is not possible at the end of the config file.
There is already a `http_top.conf`, so `root_top.conf` is a logical addition.

docker/rootfs/etc/nginx/nginx.conf

@@ -14,6 +14,9 @@ error_log /data/logs/fallback_error.log warn;
 # Includes files with directives to load dynamic modules.
 include /etc/nginx/modules/*.conf;
 
+# Custom
+include /data/nginx/custom/root_top[.]conf;
+
 events {
 	include /data/nginx/custom/events[.]conf;
 }