Explicitly set default jupyter kernel once possible.

[JWuzyk]

Address the workaround described below:

"""
@JWuzyk could you also apply this trick/workaround to automatically select the right kernel in the "settings" section in devcontainer.json:

"jupyter.kernels.excludePythonEnvironments": ["/usr/local/bin/python"]

We should probably log this as an issue to improve once the Jupyter extension allows you to configure a default kernel explicitly.
"""
Originally posted by @lsorber in #216 (comment)