Add model_name parameter for post-processing

[SamuelBrand1]

This pull request changes the model selection logic for location forecast processing by introducing model_name parameter with auto-detection of model type. This is aimed at using the S3 method approach introduced in #790 #795 .

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 41.82%. Comparing base (668ebeb) to head (34fab85).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pipelines/common_utils.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #804      +/-   ##
==========================================
- Coverage   41.85%   41.82%   -0.03%     
==========================================
  Files          30       30              
  Lines        2807     2809       +2     
==========================================
  Hits         1175     1175              
- Misses       1632     1634       +2     

Flag	Coverage Δ
hewr	37.97% <100.00%> (ø)
pipelines	36.09% <0.00%> (-0.06%)	⬇️
pyrenew_hew	62.29% <ø> (ø)

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[damonbayer]

One small nit. Thanks @SamuelBrand1!