Coverage test to be run scheduled on main -- single thread for now

A coverage test coverage-test-on-main-scheduled has been added. This is the temporary solution, using a single thread and uploading the results as an artifact. I tested it in a merge pipeline and it worked fine. I did not manage to trigger the job via schedule or by web trigger, so any help there would be appreciated. Currently it takes 23 minutes on the Ericsson runner which I suppose is fine for a scheduled job but not for the MR pipeline.