Add function to download small example datasets

[cchwala]

The approach implemented here downloads small example data from the newly created repo https://github.com/cchwala/opensense_example_data/tree/main

• solves parts of Add functionality to download small and large example datasets #56
• 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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.92%. Comparing base (61c4063) to head (2063571).
Report is 34 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##              main      #76      +/-   ##
===========================================
- Coverage   100.00%   97.92%   -2.08%     
===========================================
  Files            3        6       +3     
  Lines           43      433     +390     
===========================================
+ Hits            43      424     +381     
- Misses           0        9       +9     

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[cchwala]

Strangely, the test coverage is not 100% due to some missing lines for the plot metadata stuff, which is code I have not touched at all... Hence, I will merge this now.