The localhost is most likely a problem as well - you’ll have to replace it with the server ip of your raspery. However, if you would like to use the graph via myopenhab from remote as well a more elaborate setup will be required. You can try to set the IP - then it might accept the http:// protocol in the local network (not sure about that); but I would be surprised if this works via remote. But there are ways to get this working of course; but the setup is a bit more complex.
But step by step - do you get the graph with the ip instead of localhost - or you still see an SSL related error message in the application log?
Gives some hints about a possible setup to get interactive grafana charts working locally and from remote via myopenhab.