Co-authored-by: Saurabh Kumar <theskumar@users.noreply.github.com>
Co-authored-by: Sandeep Chauhan <sandeepsajan0@gmail.com>

Fixes #3560

Adds the settings:

```
# Should staff be able to export submissions.
SUBMISSIONS_EXPORT_ACCESS_STAFF = env.bool('SUBMISSIONS_EXPORT_ACCESS_STAFF', True)

# Should staff admins be able to export submissions.
SUBMISSIONS_EXPORT_ACCESS_STAFF_ADMIN = env.bool('SUBMISSIONS_EXPORT_ACCESS_STAFF_ADMIN', True)

```

Fixes #3242

Fixes #3021 

NEW_SUBMISSION is getting used to notify staff members on slack and also
to notify the applicant. But for draft submission, only the applicant
should get the notification, there shouldn't be any recorder activity or
slack notification.
So, added a separate event DRAFT_SUBMISSION that only sends the
notification/email to the applicant.

Co-authored-by: Fredrik Jonsson <frjo@xdeb.org>