Fix Dockerfile build and add GitHub action for testing it

[gcroci2]

• Fix Dockerfile build issue due to libstdc++.so.6 version conflict fix: dockerfile image build #637
• Add action for testing the Dockerfile. We have two options:
  • Publishing to GitHub packages: As outlined in this guide, we could publish the Docker image to GitHub Packages and then test and update the image from the CI. We decided to go for this option (PR ci: add action for releasing new docker image and testing it #640).
  • We could also add a GitHub action to automatically build and test the Docker image whenever there's a change in the .yml environment file or pyproject.toml. See also here as an example.

When this is done, do a new software patch release.

[github-actions]

This issue is stale because it has been open for 30 days with no activity.

[gcroci2]

At the moment, the Dockerfile building is broken. I am investigating what has changed.

• In particular, I get libstdc++.so.6: version GLIBCXX_3.4.29' not found` from a scipy import, even though one of the libstdc++.so.6 folders does contain such a file (the one in the conda/ folder, not the one in the system's upper root).
• I suspect that for some reason now the container can't detect the newest version of libstdc++.so.6 and points at an older one that does not contain the needed GLIBCXX_3.4.29.

When it will be fixed, I will try to create an action for building the docker image and testing it every time there is a change in the .yml environment file or in the pyproject.toml.