SelectionSort: add missing Javadoc for class and findIndexOfMin method

[JulianGStudium]

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new algorithms include a corresponding test class that validates their functionality.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

#HSFDPMUW

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.91%. Comparing base (ef986c4) to head (0f864ef).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #7494   +/-   ##
=========================================
  Coverage     79.91%   79.91%           
+ Complexity     7353     7352    -1     
=========================================
  Files           811      811           
  Lines         23879    23879           
  Branches       4705     4705           
=========================================
  Hits          19082    19082           
  Misses         4036     4036           
  Partials        761      761           

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