Expose the resolved template path

It would help a lot for OpenTelemetry Tracing integration if there is a way to retrieve the resolved template path of an endpoint.

For what I can tell, the template path is available in `org.jboss.resteasy.spi.metadata.DefaultResourceLocator#fullpath`, just not accessible from outside.

I'm happy to submit a PR, I just want to agree on how to do this.

Because the template path is associated with the current request being executed, I believe the best way is to retrieve the path using a filter. We can set things into the OpenTelemetry context on the filter to generate the span name using the template path (or `http.route`).

Possible solutions:

• Just set the attribute in the request. We already do this for things like the `ResourceMethodInvoker`.
• Expose a method in the `ResourceMethodInvoker` that can retrieve either the full path directly or `ResourceMethod`, which can be cast to `DefaultResourceMethod.
• A complete new API that can retrieve the full path, by injecting `ResourceInfo` in the filter and then using it somehow.

Any thoughts?