feat(graph): add MergeAccounts utility demonstrating email-based merging

[AlafariAbdullah]

• 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 0% with 38 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.84%. Comparing base (8930369) to head (7b3dc8e).

Files with missing lines	Patch %	Lines
...in/java/com/thealgorithms/graph/MergeAccounts.java	0.00%	38 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@ ## master #6860 +/- ## ============================================ - Coverage 78.00% 77.84% -0.16%  + Complexity 6444 6443 -1  ============================================ Files 737 738 +1 Lines 21519 21557 +38 Branches 4208 4220 +12 ============================================ - Hits 16785 16781 -4  - Misses 4062 4102 +40  - Partials 672 674 +2 

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