[recommerce] Concept for configuration files

[felix-20]

The recommerce simulation expects different configuration files for each RL-Agent.
However the API is not capable of differentiating the files:
When a configuration is send to the API, it will be written on disc. The simulation will read this file again. But the API can only write files with one generic name.
One way would be change the behaviour of the API when saving files. But translating the agent into a file name is very tedious and prone to error.
So we need the simulation to handle that.
Suggestion:
When loading a rl configuration file, the simulation will first check if this file exists. If it doesn't it will look for a file called rl_config.json and only if that does not exist, it should error.

• find all places where rl configuration files are loaded
• check if file exists before loading it
• implement fallback (so check for another file named rl_config.json) and load this file instead
• change the name the config file is saved in docker_manager.py from q_learning_config.json to rl_config.json has a needs to be fixed comment
• test if it works, including docker test