create cronitor decorator that alerts if tasks fail

make a decorator that pings cronitor before and after each task run.
Designed for use with nightly tasks, so we have visibility if they
fail. We have a bunch of cronitor monitors set up - 5 character keys
that go into a URL that we then make a GET to with a self-explanatory
url path (run/fail/complete).

the cronitor URLs are defined in the credentials repo as a dictionary
of celery task names to URL slugs. If the name passed in to the
decorator  isn't in that dict, it won't run.

to use it, all you need to do is call `@cronitor(my_task_name)`
instead of `@notify_celery.task`, and make sure that the task name and
the matching slug are included in the credentials repo (or locally,
json dumped and stored in the CRONITOR_KEYS environment variable)

tests/app/celery/test_reporting_tasks.py

@@ -20,10 +20,6 @@ from app import db
 from tests.app.db import create_service, create_template, create_notification
 
 
-def test_reporting_should_have_decorated_tasks_functions():
-    assert create_nightly_billing.__wrapped__.__name__ == 'create_nightly_billing'
-
-
 def mocker_get_rate(
     non_letter_rates, letter_rates, notification_type, date, crown=None, rate_multiplier=None, post_class="second"
 ):