add progress bar to regression models for hist fc

[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 #2061.

Summary

• Added a progress bar when performing optimized historical forecasts (retrain=False and no autoregression) to display the series-level progress.
• can be activated with verbose=True when calling ForecastingModel.historical forecasts()

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.01%. Comparing base (78d39ad) to head (8329b1e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2320      +/-   ##
==========================================
- Coverage   94.02%   94.01%   -0.02%     
==========================================
  Files         138      138              
  Lines       14191    14180      -11     
==========================================
- Hits        13343    13331      -12     
- Misses        848      849       +1     

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