[Feature] Print Queue management and time reservation

[twjdeboer]

I have a PrusaConnect instance with several printers, MK4's and an XL. Sometimes team members know that they want to print something big, usually outside of office hours. You can 'reserve' time by putting something in the queue with a delayed start, but this is not always ideal, because:

• Someone else still prints something big, this planning could be pushed back beyond closing time, meaning the print can no longer be started
• If your model is not done yet, you do not have a sliced file to 'reserve' a time slot with yet.

What I would like to propose:

• If you start a print that will push back delayed start prints, you should get a warning, maybe with the author(s) of the print(s) you are pushing back. This way you can communicate with them about delays.
• If you don't have a gcode to 'reserve' your time slot, you should be able to add a timeslot manually, estimating the duration. I now sometimes just make a placeholder gcode, but this is not ideal of course, because you risk that file actually getting printed and wasting a lot of material.
• I even think there should be an option to keep you from changing prints that you didn't start yourself, but that is another topic. This could be another permission layer.

I would love to use PrusaConnect as my one and only tool for print farm management, but there still are some issues that are holding me back. Let's work on it together!