CI: make code coverage actually usable
Code coverage was added to the CI some time ago. Up until now, a part of the result was printed at the end of the rspec test jobs, accessible via the individual job logs, barely usable.
These commits introduce deploying the HTML result and making it accessible via a dedicated page, allowing to search within and filter the data, in a much more convenient and appealing way.
While I'm not hunting for 100 percent code coverage, I think having at least a better insight into this topic is quite valuable. I hope this leads to a better understanding of our test suite, possibly identifying weak points (which then can be improved) and in the end to a better code base.