[good first issue] Automatically set room booking SETID based on current academic year

[wilhelmklopp]

Currently every year, we need to manually flip over the room bookings setid in September, otherwise the room bookings API returns stale data, see #4161

It would be good to automatically specify the setid in the settings based on the current date. I think a switch over to the new one on the 1st of September would work well.