Add LongestHappyString

[aka9ksha]

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

References

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Java files are placed inside an existing directory.
• All filenames are in all uppercase characters with no spaces or dashes.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[aka9ksha]

Added LongestHappyString

[siriak]

The code looks good, please also add some automated tests with @test. See examples in the codebase

[siddhant2002]

Can I work under this issue?

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.