TASK Add support for leaderboard as it's own microservice

[thejhh]

Goal

This support technically already is on the backend side, since leaderboard is the only stateful end point in the memory game. So our current server microservice already can act as a separated microservice, if just deployed as one.

So this task is about supporting different URL for the frontend more than else. This of course could be handled with front end proxy as a devops task as well. However, frontend support might be cleaner.