Add tensorflow-gcs-config to the tensorflow-whl build

[mcollins42]

Add a copy of tensorflow-gcs-config source and modify tensorflow-whl/Dockerfile to build the tensorflow_gcs_config wheel.

http:https://b/152051681

[rosbo]

I kicked off a CI build for the whl: https://ci.kaggle.net/job/kernels/job/docker-tensorflow-whl/job/add-tensorflow-gcs-config/

[mcollins42]

Thank you, I guess I thought that was automated.

[rosbo]

FYI: We only kick off the docker-tensorflow-whl build automatically for the branches with the -whl suffix. This is to avoid doing this 10h+ build for every single branch in this repo.

I added your branch manually to kick off the build.