Add function to download OpenRainER 8-day dataset

[cchwala]

• closes #xxxx (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks from pre-commit passed
• Added an entry in the CHANGELOG.md file

This is an extension of #89 and is based on the example data prepared in OpenSenseAction/opensense_example_data#4

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.61%. Comparing base (f1d0874) to head (c85cfcc).
Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #90      +/-   ##
==========================================
+ Coverage   98.58%   98.61%   +0.03%     
==========================================
  Files           7        7              
  Lines         635      650      +15     
==========================================
+ Hits          626      641      +15     
  Misses          9        9              

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