Periodic Discord sync tasks

[Apexal]

There's a chance that the server falls out of sync with our data, for example:

• not properly setting somebody's nickname when they join
• not properly giving the Verified role on join
• any Discord API calls getting rate limited and dropped

We can create Celery tasks that run periodically (maybe every night at midnight ET?) to ensure everything is in sync.

We can also kick off these background tasks on events like users, meetings, etc. being added/updated/deleted.