Show support to correctly derive EBL-deabsorbed spectrum

[chaimain]

Fixes #169

Changes proposed in this pull request:

• Adds data of PKS 2155-304 from gammapy-data to the additional downloadable data.
• Adds supporting functions to AsgardpyAnalysis - get_correct_intrinsic_model and get_correct_ebl_deabs_flux_points
• Follows the notebook in Gammapy PR 5275 while using Asgardpy functions

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.19%. Comparing base (71efba7) to head (db3c46f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #174      +/-   ##
==========================================
+ Coverage   99.18%   99.19%   +0.01%     
==========================================
  Files          38       38              
  Lines        2338     2372      +34     
==========================================
+ Hits         2319     2353      +34     
  Misses         19       19              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.