Allow for scaling true energy in IRFs to assess energy-scale systematics

[deborahDOR]

Modifications of the code for the consideration of systematics in the energy.
The goal is to generate modified IRFs due to the effect of a lower or higher light efficiency in the system (telescope + atmosphere) with respect to simulations, by scaling the true energy values in MC simulations.

The changes are:

• A new argument in the DataBinning Component in lstchain/io/event_selection.py : "scale true energy" (value that will be applied in the true energy values of the events of the MC files)
• Add "scale true energy" in the irf_dl3_config_tool.json in the DataBinning section (only if the value is different from 1, it will be considered in the computation).
• Changes in lstchain_create_irfs_files.py to modify the values when pyrif commands are used. Added comments to describe how it can be used and its effects.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.35%. Comparing base (7f92595) to head (e999002).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1261      +/-   ##
==========================================
+ Coverage   73.28%   73.35%   +0.07%     
==========================================
  Files         134      134              
  Lines       14084    14117      +33     
==========================================
+ Hits        10321    10356      +35     
+ Misses       3763     3761       -2     

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[morcuended]

Thanks a lot @deborahDOR, it looks good to me, I just left some comments regarding the description of the new energy scaling factor. Maybe also try to add a small unit test for this (?)

[morcuended]

Looks good! Thanks @deborahDOR and @chaimain