feat(nginx-vhosts): add support for custom nginx service command

plugins/nginx-vhosts/internal-functions

@@ -729,9 +729,13 @@ fn-nginx-vhosts-nginx-is-running() {
 fn-nginx-vhosts-nginx-init-cmd() {
   declare desc="start nginx for given distros"
   declare CMD="$1"
-  local NGINX_INIT_NAME
 
-  NGINX_INIT_NAME=nginx
+  if [[ -n "$DOKKU_NGINX_CUSTOM_CMD" ]]; then
+    $DOKKU_NGINX_CUSTOM_CMD $CMD
+    return
+  fi
+
+  local NGINX_INIT_NAME=nginx
   if fn-nginx-vhosts-uses-openresty; then
     NGINX_INIT_NAME=openresty
   fi