Description of problem:
Under the Services panel, there should be a "User Services" tab that shows the systemd user instance running on the system for the user currently logged in (including the root user, "root" also has a systemd user instance).
This would be very convenient for the user to manage his own services.
Version-Release number of selected component (if applicable):
In a shell, the systemd user instance is available through this command:
$ systemctl --user ...
Also tracked in upstream https://github.com/cockpit-project/cockpit/issues/13217