[8.x] Make urls where runway shouldn't register resources configurable

[BobWez98]

We're experiencing some 500 errors in our sentry error tracking because of the page visits at _ignition/execute-solution.

In production we would like to show a 404 page here and some of our projects display content on the 404 page that is configured in Runway field types. When Runway does not register the resources it throws a 500 error instead of a 404 error because it will land on the throwing of the ResourceNotFound exception.

This PR makes the excluded urls configurable so the intended functionality of excluding _ignition paths will still be working as it is now, but if we prefer it to be included we can.

[duncanmcclean]

Thanks for the pull request!

I think it might be better to render a 404 response when the ResourceNotFound exception is thrown, rather than add a new config option.