Change the case of X-frame-options

Ticket: https://support.gridpane.com/a/tickets/271791

Issue: IETF and MDN says use capitals for values

OLS is already using capital ones, this needs to be modified

https://gitlab.gridpane.net/gp-public/nginx-configs/-/blob/master/common/headers-http.conf#L5

We would also need a worker that sed's it from all the current sites and replaces it with capital letter one