The previous code allowed any authenticated to retreive any attachment present
on odoo filesystem. So a WMS user could technically spoken download a zip with
accounting documents.
This implementation is calling attachemnt.check("read") to ensure access
right and use attachemnt.raw attribute to retreive file to archive which
(not test) should works with attachment saved somewhere else than the
local filesystem (s3 storage, pgsql large object storage...).
