Add properties to help denote proxied collections

[briantist]

When a collection download is proxied, it becomes local in artifactory and is then indistinguishable from collections you published directly. That allows for finding and downloading those collections even if the upstream is unavailable.

But in terms of repository management, it means everything is mixed together.

If you only have one or a few namespaces for your locally published collections, like everything is company_name.collection, you can filter that way (anything not in the company_name namespace is proxied, theoretically), but it might be nice to have explicit properties for those.

For example, adding a boolean proxied property with a true or false value.
Maybe adding a source property which if blank, means direct publish, and otherwise means it was proxied from somewhere, and giving the URL of its original location.

These could be very helpful in keeping your artifactory repository clean: you may want to never delete old versions of your internal collections, while regularly culling older versions of proxied ones (if they are needed again, they will be proxied again).