ENH: Add script availability testing

[jhlegarreta]

Add script availability testing: ensure that scripts can be called by testing the call with the help flag to show the script documentation.

Add the necessary package dependencies to discover and run the tests.

Make the GHA workflow actually run the tests: uncomment the corresponding statement.

[jhlegarreta]

This is working locally. Screenshots:

And also on GitHub (24 items are collected): https://github.com/SlicerDMRI/whitematteranalysis/actions/runs/6413452971/job/17412380161?pr=154#step:5:686

So this identifies a few issues that need to be address in separate PRs:

• Some scripts do not have a main method (e.g. bin/wm_average_tract_measures.py), especially those in the utilities module, so they do not pass the checks.
• The testing/test_run.py is picked, but as no testing data exists and thus no such folder structure exists, it is failing.
• Using the more precise command to collect whitematteranalysis package tests and reporting the coverage is left for a separate PR, as it is not working, probably due to many reasons (e.g. the eggname using medial capitals: WhiteMatterAnalysis).
• The https://github.com/SlicerDMRI/whitematteranalysis/actions/runs/6413319371/job/17412053646?pr=154#step:5:730 error has to do with setuptools conflicting versions. PR #157 will hopefully help resolving this.