Provide STELLA-app with information about the systems that are (or have to be) deployed

[breuert]

When distributing requests (in the form of queries or seed documents) between experimental systems, their counters will be increased upon delivering results. Make sure pre-computed/live systems as well as ranking/recommender systems are handled separately.

• [x] Distinct between recommender and ranking systems
• [x] Distinct between experimental and baseline systems
• [x] Distinct between live and pre-computed systems At the current state, we do not distinct between live and pre-computed systems
• [x] Is it possible to read the systems from the yml-file? make environment variables w.t.h. of docker-compose.yml

[breuert]

The stella-server will write the system names into environment variables in the docker-compose file of the stella-app. When starting the stella-app, it will read out theses environment variables.

[benjwolff]

Tested. Everything works fine.