Added Goldbach's Conjecture algorithm.

[BILLSARAN]

• 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

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 73.75%. Comparing base (39122a9) to head (ab5eb79).

Files with missing lines	Patch %	Lines
...va/com/thealgorithms/maths/GoldbachConjecture.java	71.42%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6127      +/-   ##
============================================
- Coverage     73.76%   73.75%   -0.02%     
- Complexity     5122     5126       +4     
============================================
  Files           658      659       +1     
  Lines         17621    17628       +7     
  Branches       3390     3392       +2     
============================================
+ Hits          12999    13001       +2     
- Misses         4118     4120       +2     
- Partials        504      507       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[siriak]

The code looks good, could you please reuse existing algorithms for primeness check and add some JUnit tests? (see https://github.com/TheAlgorithms/Java/tree/master/src/test/java/com/thealgorithms)

[BILLSARAN]

The code looks good, could you please reuse existing algorithms for primeness check and add some JUnit tests? (see https://github.com/TheAlgorithms/Java/tree/master/src/test/java/com/thealgorithms)

I think I did it, please let me know if anything else needs to be fixed

[siriak]

Looks good, thanks!