Add new algorithm Sudoku Solver in Backtracking

[Hardvan]

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized it.
• [x] All filenames are in PascalCase.
• [x] All functions and variable names follow Java naming conventions.
• [x] All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• [x] All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 67.18750% with 21 lines in your changes missing coverage. Please review.

Project coverage is 52.36%. Comparing base (842ff52) to head (4e8bf75).

Files with missing lines	Patch %	Lines
...a/com/thealgorithms/backtracking/SudokuSolver.java	67.18%	17 Missing and 4 partials :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5524      +/-   ##
============================================
+ Coverage     52.31%   52.36%   +0.05%     
- Complexity     3259     3287      +28     
============================================
  Files           526      527       +1     
  Lines         15205    15269      +64     
  Branches       2892     2918      +26     
============================================
+ Hits           7954     7996      +42     
- Misses         6924     6941      +17     
- Partials        327      332       +5     

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