Gale-Shapley Algorithm and Tests

[BKarthik7]

Overview:
This pull request adds the implementation of the Gale-Shapley algorithm (Stable Marriage Problem) to the greedyalgorithms package. The algorithm allows for finding stable matches between two sets (men and women) based on their preferences. In addition to the algorithm, unit tests have been added to ensure correctness, and the DIRECTORY.md file has been updated to reflect this new addition.

Changes:
New Algorithm: Gale-Shapley algorithm for stable matching.
Unit Tests: JUnit tests added to validate the correctness of the Gale-Shapley algorithm with various scenarios, including multiple preferences, single pair matching, and equal preferences.
Directory Update: Updated DIRECTORY.md to include the new Gale-Shapley algorithm under the greedyalgorithms section.
Checklist:

• 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 code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 65.00000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 52.31%. Comparing base (dab8ff3) to head (c9f7944).

Files with missing lines	Patch %	Lines
...om/thealgorithms/greedyalgorithms/GaleShapley.java	65.00%	4 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5494      +/-   ##
============================================
+ Coverage     52.29%   52.31%   +0.01%     
- Complexity     3257     3260       +3     
============================================
  Files           525      526       +1     
  Lines         15185    15205      +20     
  Branches       2887     2892       +5     
============================================
+ Hits           7941     7954      +13     
- Misses         6920     6924       +4     
- Partials        324      327       +3     

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[siriak]

Looks good, thanks!