More gentle handling of accessDenieds

Summary

Students sometimes seem to be getting direct links to e.g. enqueue for a lab via e.g. Brightspace

Reasoning

They get redirected to the access denied page (via ErrorControllerAdvice) if they are not yet enrolled in that course, but in many cases they should be able to enrol and then enqueue. Hence a forward to enrol would be more friendly then putting them on Santa's naughty list.