Fix/optimized hfc prob regr

[dennisbader]

Checklist before merging this PR:

• Mentioned all issues that this PR fixes or addresses.
• Summarized the updates of this PR under Summary.
• Added an entry under Unreleased in the Changelog.

Fixes #2524.

Summary

• Fixed a bug when performing probabilistic optimized historical forecasts (num_samples > 1) with a regression models where reshaping the array resulted in a wrong order of samples across components and forecasts.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.76%. Comparing base (41e1177) to head (3ecfc2b).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2534      +/-   ##
==========================================
- Coverage   93.77%   93.76%   -0.02%     
==========================================
  Files         139      139              
  Lines       14765    14751      -14     
==========================================
- Hits        13846    13831      -15     
- Misses        919      920       +1     

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