Prevent app with duplicate routes from being deployed to Cloud

[itowlson]

The current plugin allows an app to be deployed with duplicate routes. This fails in Cloud at runtime with a ghost error. This PR makes it fail deployment.

ivan@hestia:~/testing/dup-routes$ spin cloud deploy
Error: This application contains duplicate routes, which are not allowed in Fermyon Cloud.
- Route '/...' appears in components 'dupier-routes' and 'dup-routes'

Learn more at https://developer.fermyon.com/cloud/faq

(the FAQ is unhelpful here, but cannot currently be suppressed on a case-by-case basis)