Manually triggered CI action for benchmark runs

[N-Wouda]

This is something we discussed several weeks/months ago. It would be nice to have a CI action that can run the benchmarks for us on one of our computer clusters, and report back the results.

This issue mostly serves so we do not forget about this; I do not think this is in the works for at least a little while longer.

[N-Wouda]

https://github.blog/changelog/2020-07-06-github-actions-manual-triggers-with-workflow_dispatch/

[N-Wouda]

(not sure if we still want this, but it should probably be discussed here)