Add global option to include requests in availability calculations

[orenyk]

This will definitely be blocked on #1501 (and might even be merged into it), but we've had a request for reservation requests to optionally be included when calculating equipment availability:

I have a suggestion for the Reservations site that would help us manage our requests with greater efficiency and fairness. When a student reserves an item, the equipment is still “available” to other students until we approve it. If an optional toggle could be added to block an item being requested based upon first request precedence, that would be helpful. I have been deluged with requests for break, and I can of course approve these or deny them, but this seems arbitrary from the student standpoint. Automating this seems best fro our perspective.

There is a disconnect in the student imagination between “request” and “reserved”, I am finding. A toggle that would block users from requesting previously requested items for overlapping dates would be helpful. I personally think a global option for my sites would be best, but I can also see a case for having the option on a case-by-case basis.

I can see a use case for this, although I suggested that perhaps they update their equipment limits so that requests were more infrequent. It will hopefully be fairly straightforward as we can just add the relevant logic to the active query and tweak it based on an app config. Thoughts?