Added MinimumWindowSubstring algorithm and test (Sliding Window)

[jaimin45-art]

• 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

❌ Patch coverage is 86.20690% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.87%. Comparing base (4858ec9) to head (a00458c).

Files with missing lines	Patch %	Lines
.../thealgorithms/strings/MinimumWindowSubstring.java	86.20%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6813      +/-   ##
============================================
+ Coverage     77.85%   77.87%   +0.02%     
- Complexity     6359     6372      +13     
============================================
  Files           731      732       +1     
  Lines         21187    21216      +29     
  Branches       4140     4149       +9     
============================================
+ Hits          16495    16522      +27     
- Misses         4034     4035       +1     
- Partials        658      659       +1     

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