Handle giving groups access to offices correctly

[adehnert]

Right now, I *think* that if you add a SpaceAssignment? for a group, it won't trigger anything in the emails to CAC. This isn't a disaster, but it's certainly suboptimal. Really, that should trigger telling CAC "here are all the people in the group; please add them", possibly with a note explicitly acknowledging that the group just moved in.

I believe that this is the cause of the mstew issue in ​https://help.mit.edu/Ticket/Display.html?id=1978318 --- he was added to Shared Storage Access in the DB the same day we created all the space assignments, but after I had generated the CSV file I sent CAC.