[Route] Ensure @Route.service is not defined on methods (fix #192)

| Q             | A
| ------------- | ---
| Bug fix?      | yes/no, throw an exception rather than silently ignore the service option
| New feature?  | yes, throw an exception rather than silently ignore the service option
| BC breaks?    | kind of if the configuration was wrong
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #192
| License       | MIT
| Doc PR        | -