Reference results: Archive Python environment information

[MakisH]

As suggested by @fsimonis, we can use pip freeze to get a tree of all dependencies used in a venv:

https://pip.pypa.io/en/stable/cli/pip_freeze/

[MakisH]

A file pip-installed-packages.log is included in all Python-related tutorials since #608.

Missing is including this in the reference results. This, however, would break many assumptions that we currently have in what we consider as reference results and how we archive them. We currently only consider the precice-exports/, which are defined per tutorial, while this file is defined per case.

In general, more files and potentially the complete results would be useful to be archived as reference results for debugging purposes. But this would increase the storage requirements a lot (even if we use Git LFS, getting the repository would download multiple multi-MB files), and would require several changes in the way we archive things.

As a much easier and more useful work-around, I suggest (manually) archiving the full build artifact outside this repository. For this reason, I have now included the run number in the name of the artifacts in #628. When someone triggers the generation of new reference results, they could also archive the complete artifact (since these are retained by GitHub for up to 90 days).

I will address this again in #629, in the context of #400, update the related documentation, and add reminders. Closing for now.