Clearer definitions for Open Match terms

Terms like `MatchProfile` and even `Ticket` are taken for granted, either explained in the middle of a tutorial or deep in the API reference. I originally went to the Glossary after encountering "MatchProfile" with no other context around it, but only found generic cloud terms there. The Glossary may be a great place to add Open Match specific terms as well as a singular reference point.

I'm willing to do this work, but I want to make sure it's wanted before I start.