Reorganize configuration file contents

[HealthyPear]

The current config file is a bit monolithic given the porting from the legacy script.

I think it should be a bit more organized with less coarse sections:

• observation, for properties related to the observatory, constraints and datetime
• source, for properties related to the assumed source like spectrum, extension, etc...
• analysis, for properties related to the actual performance computation
• plotting, for estetics settings