make it so the list of available software images is configured in admin settings, e.g., via a publicly available file

[williamstein]

When I modify compute server configuration I change this one field in admin configuration:

In the screenshot, it's pointing to a raw file in a git repo, but it could be anything (that's just what I happen to use right now).

In contrast, for project image configuration, we still just directly edit the cocalc source code like here:

#8047

That was OK for a time, but is clearly not a great approach, especially since there are more and more installs of cocalc for which their project images have nothing to do with ours. Also, it's not optimal to have to build a whole new frontend to make these changes. Instead, just copy what's done for compute server configuration, which is much more flexible.

[williamstein]

NOTE: I think the external file is used once to populate the database when that button is clicked, and not otherwise. It's important that it's not a hard dependency for cocalc.com to run.