This way, we need not list every value again to create the enum.
N.B.: enum values are now accessed as `models.NotificationType.FOO`,
instead of `models.Notification.FOO`.
This is essentially a revert of 9cbff312a. The commit was at the advice
of the Celery docs for optimization, but I've since decided that the
downsides in terms of making things harder to debug (it makes Flower
nearly useless, for instance) are bigger than the upsides in performance
gain (which seem extremely small in practice, given how long our tasks
take, and the number of tasks we have).
Since we don't use the results of our Celery tasks (all of them return
None implicitly), it's prudent to set the ignore_result flag, for a
potential performance improvement. See the Celery docs for details [1].
We could do this with the global CELERY_IGNORE_RESULT setting, but it
offers more flexibility if we want to use task results in the future to
set it on a per-task basis.
[1]: https://docs.celeryq.dev/en/stable/userguide/tasks.html#ignore-results-you-don-t-want
