allow to trigger tests remotely and run in webknossos CI

[jstriebel]

To test the webknossos - webknossos-libs compatibility we could trigger webknossos-libs CI runs (which should use the correct wk docker images) from the webknossos repo and show the result in the webknossos PR CI again. Alternatively, we also might run some tests directly in the webknossos CI, but this seems rather fragile.