Draft: Add commands for coverage report

Follow up on #1 with options used in PDELab. At the moment, the compilation with code coverage support is still missing. We need to add the flag --coverage and link against gcov to make this functional. Feel free to propose alternatives.

Note: nothing is tested yet, and I am assuming that gcov-12 exists in the debian 12 image. I am sure gcov-10 exists in the debian 11 image, but I think it would be nice to combine this with the checkings in the debian 12 image. So some further tests are needed.