Add placeholder testsuite for gnome shell
The GNOME Shell team have their own testing infrastructure - see https://blogs.gnome.org/shell-dev/2022/12/02/automated-testing-of-gnome-shell/
It's not immediately obvious how to combine this with openQA and get the best of both worlds. In the meantime, a placeholder test for the Shell that just opens the activities overview and runs a search would be a nice demo of how openQA-based test infra can work for the Shell,