[11.x] Hide X-powered-by in nginx config for deployment

[me-shaon]

It is recommended in the OWASP guide to hide the X-Powered-by header in the web server config. https://cheatsheetseries.owasp.org/cheatsheets/HTTP_Headers_Cheat_Sheet.html#x-powered-by

That's why I've updated the nginx config given in the Deployment section to add a directive for this.