api: data in the error template shows the URL behind the reverse proxy
When getting a 404 error because of an object not found, the "Request" mirrored by the API shows the internal URL rather than the external one.
Reproducer : https://archive.softwareheritage.org/api/1/origin/deb/url/deb://Debian-Security/openldap
The "Request" area shows :
GET http://127.0.0.1:5003/api/1/origin/deb/url/deb://Debian-Security/openldapinstead of
GET https://archive.softwareheritage.org/api/1/origin/deb/url/deb://Debian-Security/openldapMigrated from T806 (view on Phabricator)