ImagePush: print image reference to stdout on success (#1470)

-Resolves #1466.
- `container image push <ref>` previously produced no
  standard output on success. Print the fully qualified
  reference (`image.reference`) after the push completes
  so callers can pipe the output into subsequent
  commands.

Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>

Sources/ContainerCommands/Image/ImagePush.swift

@@ -75,6 +75,7 @@ extension Application {
             progress.start()
             _ = try await image.push(platform: p, scheme: scheme, progressUpdate: progress.handler)
             progress.finish()
+            print(image.reference)
         }
     }
 }