Allow CORS mocking

It would be nice if the REST simulator had support for mocking / doing CORS.
It's easy enough to do it now by registering a HandlerInterceptor, but it would be nice if this kind of thing could be provided out-of-the-box:
```
public class CorsHandlerInterceptor extends HandlerInterceptorAdapter {

@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
if (CorsUtils.isCorsRequest(request)) {
response.setHeader(HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN, "*");
response.setHeader(HttpHeaders.ACCESS_CONTROL_ALLOW_METHODS, "*");
response.setHeader(HttpHeaders.ACCESS_CONTROL_ALLOW_HEADERS, "*");
if (CorsUtils.isPreFlightRequest(request)) {
return false;
}
}

return true;
}
}
```

Start by locating the REST simulator's request handling and the HandlerInterceptorAdapter integration. Review the provided CorsUtils, HttpHeaders, and preflight behavior as the reference for CORS mocking. Done means CORS requests receive the specified headers and preflight requests are handled without reaching the simulator.

Written by the indexing model from the issue text.