YaST service manager can't enable foo@.service (service files with parameters,
for example openvpn@.service

If I select "openvpn@", click "Start/Stop" to start it and then "OK" to
actually start it, I get an error message (translated back from german)

    Writing the configuration failed:
    openvpn@ can't be enabled. Failed to get properties: 
        Unit name openvpn@.service is not valid.

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Expected behaviour: When someone tries to enable a foo@ service, ask for the
parameter to use (= display an input field) and then enable
foo@<userinput>.service.


(not attaching any logs because this is very obvious and easy to reproduce)