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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