Add NbConvert Action for Jupyter Notebooks

Convert Jupyter Notebook (ipynb) files into Python executables. Code scan with Saftey and Bandit.

This is mainly to maintain feature parity with [ASH](https://github.com/aws-samples/automated-security-helper), but Jupyter notebooks are probably not one of the main types of deliverables used by ProServe (not in top 80%).

Review the repository's existing GitHub Actions and the linked ASH implementation before deciding where the notebook conversion belongs. The work is complete when Jupyter Notebook files are converted into Python executables and the resulting code is scanned with Safety and Bandit.

Written by the indexing model from the issue text.