feat: implement proxy-clear-config

This will allow us to kill stale proxy configuration within apps, which is critical during application renames.

- redirect rmdir output to dev-null
- trigger a proxy-clear-config (new trigger) when renaming an application
  - The configuration will be rebuilt during the later `ps_rebuild`

Closes #3231

plugins/nginx-vhosts/internal-functions

@@ -26,3 +26,9 @@ nginx_vhosts_help_cmd() {
 help_desc
   fi
 }
+
+nginx_clear_config() {
+  declare desc="Remove the nginx conf file"
+  declare APP="$1";
+  rm -f "$DOKKU_ROOT/$APP/nginx.conf"
+}