Soon enough every service will have this permission, and they won’t be
able to switch it off. So we should clean up our codebase and make it
so there’s no dependancy on a row existing in the permissions table.
This is the first step of that process for the API. Before we can remove
it, we have to stop checking from it. Next step will be to stop
inserting the permission, then finally remove it from the database.
When a precompiled letter is sent via the admin app, we now pass in the address which can be set in the Notifications.to field.
Once a precompiled letters sent by the API has passed validation we can set the address in Notifications.to field.
The celery tasks to validate precompiled letters sent by the API will be done in another PR.
This function checks various permissions, downloads the PDF from the
transient bucket, creates the notification then moves the letter to the
'normal' bucket.
