Add METIS notebooks to the CI

[hugobuddel]

Branch https://github.com/AstarVienna/irdb/tree/hb/runmetisnotebooksinci also runs the METIS notebooks in the CI.

(There is no PR yet, because the notebooks are skipped when automatically running the CI on a PR. Instead, manually trigger the action, then the notebooks are run.)

However, they fail, probably because they use too much memory. Using /usr/bin/time -v on my machine shows that https://github.com/AstarVienna/irdb/blob/dev_master/METIS/docs/example_notebooks/LSS_AGN-02_simulation.ipynb uses 13 GB of RAM, which seems to be over the github action limit.

I believe that is also the notebook that I cannot run on my 16 GB RAM laptop. There are probably more users with a similar laptop, so maybe it would be a better user experience if we make the notebook simpler.

@astronomyk what do you think?

[hugobuddel]

Increasing the spectral bandwidth by a factor 2 to 3.0e-3 reduced the memory footprint by a factor 2 as well, and doesn't seem to affect the plots noticibly. First with 1.5e-3:

Then with 3e-3: