Add a verbose test logs checkbox to integration scheduler

We'd like to reduce the amount of output shown in the ci test log using this change
https://codereview.qt-project.org/c/qt/qtbase/+/446504/2

But sometimes developers might want to see the full verbose output.

We could achieve that by adding an extra checkbox to the integration scheduler, "Enable verbose test logs".
Enabling that would set an environment variable that can be checked by qtbase's test run instructions, to pass either --verbose or --output-on-failure command options to ctest.