Fixing MNIST dataloader

[tihbe]

tutorials/end_to_end/tutorial01_mnist_digit_classification.ipynb doesn't work if you install lava with a pip install as mnist.npy is not packaged. I fixed it by completing these to-dos.

[mgkwill]

@tihbe Thanks for the pull request!

We generally require an issue for each pull request describing the intent of the PR linked to the PR.

Beside that, it looks like you have a bandit security linting issue. Please run bandit -r src/lava/ --format custom --msg-template and fix the issue in question. I've assigned some reviewers.

[tihbe]

@mgkwill Thanks for the info ! Did you want me to create an issue for this PR first ?
I'm not 100% sure how to fix the security linter issue. It seems that using urllib.request.urlopen automatically triggers the linter. I've disabled the specific line triggering the error as suggested here.

[mgkwill]

Thanks for the updates @tihbe and trying to sort out the bandit security linting issues.

[srrisbud]

@tihbe, have you addressed the change requested by @mgkwill?

[tihbe]

@srrisbud Yes