Start kernel automatically without prompting

[martinRenou]

Remove the "Choose kernel" prompt by starting the default kernel automatically. This only works if the default kernel is a Python kernel.

Doing this triggered a race condition where viewers would be created before the GLUE_SESSION was created, this PR fixes this race condition as well.

[github-actions[bot]]

:point_left: Launch a Binder on branch _martinRenou/glue-lab/start_kernelautomatically

[trungleduc]

Thanks!