Add Minimum Window Substring algorithm in Sliding Window package (#6553)

* Create MinimumWindowSubstring.java

* Create MinimumWindowSubstringTest.java

* correct MinimumWindowSubstringTest.java

* Added more test cases

* Update MinimumWindowSubstringTest.java

* Update MinimumWindowSubstringTest.java

* Update MinimumWindowSubstringTest.java

* Update MinimumWindowSubstringTest.java

* Update MinimumWindowSubstringTest.java

* Update MinimumWindowSubstringTest.java

* Added test case "AAABBC" "AABC"

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Co-authored-by: Deniz Altunkapan <93663085+DenizAltunkapan@users.noreply.github.com>