Provide a way of distinguishing between user types

[miparnisari]

We don't have a good way to distinguish between different user types (user:x, group:x#member, and user:*) in a strongly typed way and so in ListObjects we are forced to do this:

https://github.com/openfga/openfga/blob/e9bd83df3f61550d1704e14abbb47a2474cb8abf/pkg/server/commands/connected_objects.go#L30C1-L83