Automate image builds of Jupyter UI

[kimwnasptd]

We need to update the jupyter-web-app's image in gcr to include the changes made in this PR, in order to redirect to the correct URL for the notebook.

[jlewi]

@kimwnasptd Are we not building and pushing the jupyter image on postsubmit?

[kimwnasptd]

By taking a look here the image was build only twice including the one done by hand (I guess?) yesterday.
My mentioned PR changed two .js files in the components/jupyter-web-app dir. Is there a process/mechanism looking for changes under the components dir that builds the new images automatically?

[jlewi]

We should define an E2E test that builds the image automatically.

Some instructions here
https://github.com/kubeflow/kubeflow/blob/master/docs_dev/releasing.md#image-auto-release

On presubmit the image should be pushed to gcr.io/kubeflow-ci.
On postsubmt the image should be pushed to gcr.io/kubeflow-images-public

I would suggest using GCB to build the images (that seems to work better than using Docker in Docker or Kaniko).

The mnist jsonnet workflow might be a good place to start.
https://github.com/kubeflow/examples/blob/master/test/workflows/components/mnist.jsonnet

We probably just need the steps to checkout the repos and build the image using GCB.

[kimwnasptd]

/assign @kimwnasptd

[jlewi]

@kimwnasptd I believe we updated the notebook manager image. Is this issue now tracking automating builds of the notebook manager UI? If so should we update the title to reflect that?