Ohhhh boy, yeah. I requested this back in April.
The most frustrating thing is, the feature actually DOES already exist, you just need to do it via a different mechanism, which is deeply frustrating.
If you have an ‘event trigger’ which is defined on the folder level in the Orchestrator, rather than the Integration Service, than you have this kind of control, including job priority which is also missing here.
I can only tell you how mad I was when I found this out myself after trying to communicate this need directly to the product team and from trying to follow the instructions, I have tried my best to get the documentation updated, but hopefully this topic can help also redirect people as that hasn’t happened.
Now, that being said, creating an event trigger. I have done this in the past, but the option is greyed out now, and I am not sure why.
I think you have to do it by adding a trigger activity to the start of your workflow in you Main in Studio, and when you publish the package I think you can then make this event trigger in the folder and have this control.
Edit: I double checked, the machine and user actually also cannot be set here, the priority can here though which cannot be done via the integration service 
Sorry
