Improved docs for NDSL examples

[romanc]

Description

Tutorials are in important step in on-boarding new library users. While working through the examples, I noticed a couple of typos and broken links. In the bigger picture, we figured that examples should use the boilerplate code that the middleware already exposes in ndsl.boilerplate. I've also added a README file with a little bit of context and a quickstart guide to get people up and running with minimal overhead. And we agreed to remove the output currently stored in the Jupyter notebooks. This was one in the first commit such that we can see the actual changes when looking at the other commits.

In summary

• Removed all output from the Jupyter notebooks
• Moved plot_filed_at_kN from examples/NDSL/basic_boilerplate.py to ndsl/boilerplate.py. This adds matplotlib to the list of dependnecies.
• Refactored Jupyter notebooks get all boilerplate code from ndsl.boilerplate.
• Removed examples/NDSL/*_boilerplate.py
• Added examples/NDSL/README.md with a bit of context.
• Fixed typos and broken links in Jupyter notebooks.

It is recommended to exclude the first commit when looking at the diff, e.g. this view is much nicer to look at.

Regarding the previous addition of a .tool-versions file a python version manager: With the install instructions as simple as pip install ndsl[demos], I don't think we need this complexity anymore. The middleware's README already specifies the need for python 3.11. How developers ensure this should be up to them.

Fixes: N/A

How Has This Been Tested?

I ran all the notebooks locally against a local version of NDSL.

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [ ] Any dependent changes have been merged and published in downstream modules
• [ ] New check tests, if applicable, are included

[romanc]

Sorry, for yet another commit. Just realized that one of the notebooks was marked as executable