Prior to this change, there were reports of 500s in
production due to `export.extra_data` being a
Nonetype. This was reproducible using the s3
backend in development when a row was created in
the `RealmAuditLog` table, but the export failed in
the `DeferredWorker`. This left an entry lying
about that was never updated with an `extra_data`
field.
To fix this, we catch any exceptions in the
`DeferredWorker`, and then update `extra_data` to
encode the failure. We also fix the fact that we
never updated the export UI table with pending exports.
These changes also negated the use for the somewhat
hacky `clear_success_banner` logic.
Apparently, the Zulip notifications (and resulting emails) were
correct, but the download links inside the Zulip UI were incorrectly
not including S3 prefix on the URL, making them not work.
While we're at this, we rewrite the somewhat convoluted previous
system for formatting the data export output.
Wyatt Hoodes
Tim Abbott
Thomas Ip