Added Sudoku Solver algorithm in backtrackingpackage

[codewithRakshita]

• 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 78.20%. Comparing base (0837424) to head (40f87e2).

Files with missing lines	Patch %	Lines
...a/com/thealgorithms/backtracking/SudokuSolver.java	0.00%	38 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7020      +/-   ##
============================================
- Coverage     78.34%   78.20%   -0.14%     
  Complexity     6621     6621              
============================================
  Files           747      748       +1     
  Lines         22036    22074      +38     
  Branches       4322     4335      +13     
============================================
  Hits          17264    17264              
- Misses         4085     4123      +38     
  Partials        687      687              

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