Investigate bulk_save_objects for notification inserts

[terrazoon]

Description

The next roadblock on scaling up to millions of notifications a day is the fact that we current insert notifications to the db one at a time. Try batch inserts using redis, a scheduled task, and bulk_save_objects().

So instead of writing one at a time to the db, and immediately sending to AWS afterwards, we:

1. write to redis
2. after writing to redis, send the notifications to AWS on a delay (60 seconds). It's on a delay so there is enough time to get the notifications written to the db before we need to process the sending.
3. every 10 seconds, grab notifications from redis and batch write to the db

Security Considerations

With this new approach, notifications would held in redis for 10-50 seconds, meaning potentially there could be a few hundred notifications in redis at any particular time when big sends are happening.

[ccostino]

Awesome, thanks @terrazoon!

There were some general questions I had, and this is just for the saves/inserts - not any updates, right?

Thanks for writing/updating all of the tests, too, those look good!

[ccostino]

Awesome, everything looks good to me now @terrazoon, thank you!