Make performance datasets choice more flexible

[HealthyPear]

Right now it is all based on MAGIC data since the original script was developed there

if we want to add support for other instruments (e.g. LST) or a combination of instruments the configuration file section should be more flexible allowing us to choose an instrument and zenith range (observation time is already there)

instrument: MAGIC
zenith_range: mid
observation_time: 50 h

Any specific choice will point to a specific dataset which should be described in the documentation.