Add an endpoint to cancel a job

If you schedule a job you might change your mind or circumstances might
change. So you need to be able to cancel it. This commit adds a `POST`
endpoint for individual jobs which sets their status to `cancelled`.

This also means adding a new status of `cancelled`, so there’s a
migration…

tests/app/dao/test_jobs_dao.py

@@ -7,6 +7,7 @@ from app.dao.jobs_dao import (
     dao_update_job,
     dao_get_jobs_by_service_id,
     dao_get_scheduled_jobs,
+    dao_get_future_scheduled_job_by_id_and_service_id,
     dao_get_notification_outcomes_for_job
 )
 
@@ -251,3 +252,10 @@ def test_get_scheduled_jobs_gets_ignores_jobs_scheduled_in_the_future(notify_db,
     sample_job(notify_db, notify_db_session, scheduled_for=one_minute_in_the_future, job_status='scheduled')
     jobs = dao_get_scheduled_jobs()
     assert len(jobs) == 0
+
+
+def test_get_future_scheduled_job_gets_a_job_yet_to_send(notify_db, notify_db_session):
+    one_hour_from_now = datetime.utcnow() + timedelta(minutes=60)
+    job = sample_job(notify_db, notify_db_session, scheduled_for=one_hour_from_now, job_status='scheduled')
+    result = dao_get_future_scheduled_job_by_id_and_service_id(job.id, job.service_id)
+    assert result.id == job.id