Refactor: write log events asynchronously via celery queue

[jayaddison]

Describe the reason for these changes and the problem that they solve

Instead of synchronously writing event logs during API request processing, we should queue the events to be written to the database later.

Briefly summarize the changes

1. Write the event type and fields to a celery task queue instead of directly to the database

List any issues that this change relates to
Relates to openculinary/infrastructure#8