Fix Memory Usage when fetching graphs overview

[MaxKissgen]

When a user, for example through the webclients graph table, fetches the overview of all graphs over the ocd/graphs endpoint, an overly large amount of memory seems to be accessed just for getting the necessary superficial information for these graphs.
Especially when a user builds a larger collection of graphs this can lead to longer loading times for the overview and in the worst case overwhelm the service.
Calling this endpoint therefore needs to consume much less graph memory