Make binary fields default to attachment=True #29308
Because custom/studio doesn't provide for specifying this parameter (and it's unclear how this could be handled e.g. what if a user decided to switch back and forth between attachment and not attachment?) custom binary fields are currently created with attachment=False, and since they're mostly used to associate images or documents to records that quickly bloats database's on-disk and backup sizes without the ability to hardlink/dedup provided by the filestore.
Flip the default, and adapt the existing binary fields.