Adding tests for juypterhub-ssh, jhub-client, and vs code

[costrouc]

From my testing jupyterhub-ssh does not fully work as an expected ssh session. Currently it is hanging at times with

/opt/conda/condabin/conda
/opt/conda/condabin/conda

And then hanging and not giving a shell.

[review-notebook-app]

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[danlester]

Looks good, although would be good not to have to start/stop the JupyterLab server for every test - I guess we can work on that if we add extra tests such as for Dask Gateway.

[costrouc]

@danlester I agree. This would make the tests faster. But I don't know how we can get around this since in the UI tests we want to test the start and stop button. So this will require that at a minimum we start and stop twice.

[danlester]

Yes, this was one reason I built the Python tests into Cypress initially - click to Start, then run the tests, then stop!

But as long as multiple notebooks can be done in one session, maybe that's OK.

[costrouc]

Ah that makes perfect sense. The pytest test_deployments will also need to launch servers but this was added with this PR as well. Do agree that starting/stoping costs around 15-30 seconds in the CI