Improve the relay integration test.
Improve the relay integration test.

- add instructions for how to run the relay test locally
- use a separate kubeconfig

Change-Id: Ia66a2bf88828b3d3b16a87c2d3f322381dec54be
GitOrigin-RevId: d875e3a3909fed3c0053459311c0b291f38cda06

googlecloudrobotics/core,googlecloudrobotics/core,googlecloudrobotics/core