Preserve pathname prefix in re_uri #10373
Description
We currently fail to parse URLs like rerun+http://13.31.13.31/rerun/proxy. We probably should be more lenient and allow this, because we can always tack more pathname segments at the end.
After parsing, we should keep the original pathname around minus the endpoint, e.g. the above will become http://13.31.13.31/rerun. An example gRPC client request to that URL is POST http://13.31.13.31/rerun/rerun.v1alpha1.sdk_comms.MessageProxyService/ReadMessages. As long as /rerun/* is proxied to the gRPC server with the path rewritten to /rerun.v1alpha1.sdk_comms.MessageProxyService/ReadMessages, that should be enough.