Odd combination of 404 error and "Add Data" button with only Dataset Creator role on a collection

@sbarbosadataverse @scolapasta and I talked about this in the context of troubleshooting a problem for CAFE (ticket, googe group thread, Slack thread 1, Slack thread 2).

To troubleshoot, I asked for the Dataset Creator role on an unpublished collection. Here's how it looks in the SPA:

This is actually much better than JSF which doesn't give you a button to add a dataset.

However, the combination of a 404 error and working buttons "Add Data" buttons makes for a strange user experience.

A workaround it to also give the read-only "Member" role to the user. However, this will, of course, let the user see the contents of the collection, which may not be desired.

Start by reproducing the SPA view with only the Dataset Creator role on an unpublished collection, then trace the source of the 404 and the conditions that show the Add Data buttons. Compare the result with the Member-role workaround and the JSF behavior. Done means the collection view presents consistent access feedback without exposing restricted collection contents.