Optionally include notifications from jobs

Previously we would exclude these. We have a service [1] that:

- Uses the API to send initially.
- Uses the API to query failures.
- Uses the UI to manually resend.
- Uses the API to check the results.

While I'm not entirely convinced the last step is necessary, it
_is_ confhsing that what's visible in the UI is inconsistent with
the result from the API client. So, for at least that reason, this
adds the option to include notifications sent via a job.

Note that our Ruby client implicitly allows this already, by not
restricting the set of allowed parameters [2].

[1]: 53be32cd-69c1-4a72-a2e8-46ad8f768c61
[2]: https://github.com/alphagov/notifications-ruby-client/blob/328362a2df82cc0cb142618065467a032416cbd3/lib/notifications/client.rb#L101