Since Workhorse started accelerating attachments in the upload API
(https://gitlab.com/gitlab-org/gitlab/-/merge_requests/57250), the
`content_length` log in `api_json.log` no longer holds the actual bytes
used by the uploaded file. It now reports the number of bytes from the
Workhorse JSON metadata.

In order to determine which projects might be exceeding this limit, we
log a JSON warning that will make it easier to fill in the allow list
for https://gitlab.com/gitlab-org/gitlab/-/issues/325788.