feat: Added digital root algorithm(also with recursion)

[ankana2113]

 know more

Describe your change:

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

Checklist:

• [X] I have read CONTRIBUTING.md.
• [X] This pull request is all my own work -- I have not plagiarized.
• [X] I know that pull requests will not be merged if they fail the automated tests.
• [X] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [X] All new JavaScript files are placed inside an existing directory.
• [X] All filenames should use the UpperCamelCase (PascalCase) style. There should be no spaces in filenames. Example:UserProfile.js is allowed but userprofile.js,Userprofile.js,user-Profile.js,userProfile.js are not
• [ ] All new algorithms have a URL in their comments that points to Wikipedia or another similar explanation.
• [X] If this pull request resolves one or more open issues then the commit message contains Fixes: #1747 .