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 79.88%. Comparing base (51137a1) to head (51d9f3e).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7494      +/-   ##
============================================
- Coverage     79.89%   79.88%   -0.02%     
+ Complexity     7344     7341       -3     
============================================
  Files           809      809              
  Lines         23850    23850              
  Branches       4699     4699              
============================================
- Hits          19055    19052       -3     
  Misses         4036     4036              
- Partials        759      762       +3     

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