Adding PiApproximation algo

[the-yash-rajput]

• 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 89.47368% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.30%. Comparing base (5f8d8ee) to head (115d87f).

Files with missing lines	Patch %	Lines
.../java/com/thealgorithms/maths/PiApproximation.java	89.47%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6602      +/-   ##
============================================
+ Coverage     76.29%   76.30%   +0.01%     
- Complexity     5914     5919       +5     
============================================
  Files           709      710       +1     
  Lines         20111    20130      +19     
  Branches       3899     3902       +3     
============================================
+ Hits          15343    15360      +17     
- Misses         4177     4179       +2     
  Partials        591      591              

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[the-yash-rajput]

@alxkm Can you please review this one too?

[DenizAltunkapan]

Looks good. Thank you!