The code was looking for `original_file_name` in the metadata for a
contact list, or the query string if it wasn't in the metadata. Now that
the change to use the metadata for the file name has been deployed for a
while e can stop looking in the query string for the
`original_file_name`.
We were passing `original_file_name` from the `.upload_contact_list`
view function to the `.check_contact_list` view function as a query
param. We now store it in the metadata instead. `.check_contact_list`
still checks for `original_file_name` in the query string if it's not in
the metadata - this is necessary until the code has been deployed for a
few days and we can be sure that there are no contact lists that are
mid-way through the upload stage.
the upload preview page has a file_id - this corresponds to the file in
the transient pdf uploads bucket. However, if the user already hit send
(and then navigated back) the file's no longer in that bcuket, it's been
moved to the regular letters-pdf bucket. So the s3 get request fails. To
avoid this, simply redirect to the notifications page if the file isn't
in the transient bucket. This is better for the user as it'll stop them
trying to submit it twice, and will provide more clarity on the status
of the notification too.
