feat: add nginx:reload command

Reloads the nginx server config after validating it with `nginx -t`. Useful for picking up changes to globally managed nginx configs without restarting the running process.

plugins/nginx-vhosts/subcommands/reload

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+source "$PLUGIN_AVAILABLE_PATH/nginx-vhosts/command-functions"
+set -eo pipefail
+[[ $DOKKU_TRACE ]] && set -x
+
+cmd-nginx-reload "$@"