Hackathon Regions

Currently, the code for determining the region of a hackathon is [located in the front-end repo](https://github.com/hackclub/hackathons/blob/1ad8ff8696cbdcacb4d04feb34084ec8f3cafdb8/pages/%5Bregion%5D.js#L51
). Let's move this to the backend.

The Airtable contained an `apac` boolean, which was also migrated over this repo as a temporary solution. The new `Hackathon::Region` model should phase out the use of that boolean. (At the moment it's also exposed via the API to maintain existing functionality on the front end)