Automated unit tests for tutorials

[mathisrichter]

User story

As a developer of lava-dl, I want to have automated unit tests for all Jupyter notebook based tutorials to ensure they do not break.

Conditions of satisfaction

• All Jupyter notebook tutorials have a unit test that is automatically run in CI

[bamsumit]

Thanks @mathisrichter I'll create them, at least for inference notebooks.

Training notebooks specifically require GPUs and take hours to complete. That's why we never added notebooks to the unittests. The networks in inference notebooks are already covered by their specific unittests.

We should setup a weekly/biweekly regression to test these long running scenarios once we setup running the tests on Kubernetes cluster with GPU.