Add "Add discid" edits in release artist(s) editing history

I think the "Add discid" edit type should be related to release artist(s), like it was pre-NGS.
Furthermore:

• It helps reviewing added releases (discid(s) presence is a good indication of reliability).
• It can be interesting to review where discid is attached to existing release, now that tracklist are shared (a discid may belong to only one edition, ...)