Added Circular Doubly Linked List in the datastructures section

[richk21]

• 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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.23%. Comparing base (421ac6d) to head (9eacb59).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6565      +/-   ##
============================================
+ Coverage     75.19%   75.23%   +0.04%     
- Complexity     5614     5626      +12     
============================================
  Files           690      691       +1     
  Lines         19407    19448      +41     
  Branches       3755     3758       +3     
============================================
+ Hits          14593    14632      +39     
- Misses         4247     4248       +1     
- Partials        567      568       +1     

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[richk21]

Doubly Circular Linked List Geeks for Geeks link:
https://www.geeksforgeeks.org/dsa/introduction-to-circular-doubly-linked-list/

[alxkm]

Looks good! Thanks for the contribution.