Test that installed examples actually run

I have hit several bugs lately while trying to compile all of qt6 and run examples. Build doesn't configure, or examples are missing files after installation etc.

One way is to have a nightly build that configures/compiles/installs the qt6 supermodule and makes sure that the examples at least execute without crashing.

1. clone qt5 repo
2. perl init-repository
3. configure -make examples -prefix /opt/whatever
4. ninja && ninja install
5. As a next step, a script can spawn every example in the installation directory and kill it after 10s, while checking the exit code, i.e. try to detect if some example crashes.