Confirm that trying a route which does not exist results in a not found error that matches OC

[oliverheywood451]

This issue is about what happens if you try to hit a middleware route which does not exist. What should happen in that scenario is the the status should be 404 and there should be an error body with the message "Not Found" which matches OrderCloud's not found error.

I'm not sure if that's working correctly now or not. Either way, there needs to be an integration test for this scenario.