Make s.Pagetype accessible in Processing Rules

We use a singular code base across the site, rather than static tagging. Generally, we use Processing rules to help manage some exception handling.  the 404Error page is one such exception

In debugger, regardless of the bad URL, the page title is "page not found"

with s.pagetype available in Processing rules, we could create

IF Page Title is "page not found".

Overwrite value of s.pagetype="errorPage"