add cable trace (pathing) for front-ports and rear-ports

[marcelb98]

The Netbox API has no /trace endpoint for front-ports and rear-ports, but a /paths endpoint (see issue #434). This PR implements the /paths endpoint for pynetbox.

[srfwx]

Hi, I've tested your code. It doesn't work for me when tracing an open path. I think a condition is missing in case there is no origin/destination port.

origin_endpoint = "/".join(
                    urlsplit(origin["url"])
                        .path[len(urlsplit(self.api.base_url).path):]
                        .split("/")[1:3]
                ) if origin else None

destination_endpoint = "/".join(
               urlsplit(destination["url"])
                   .path[len(urlsplit(self.api.base_url).path):]
                   .split("/")[1:3]
           ) if destination else None