feat: Add implementation for Armstrong number check

[AmanxUpadhyay]

Description of Change

This pull request includes the addition of a new program to check if a number is an Armstrong number. The changes introduce a new file others/armstrong_number.cpp with the implementation details.

Checklist

• Added description of change
• Added file name matches File name guidelines
• Added documentation so that the program is self-explanatory and educational - Doxygen guidelines
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
• Search previous suggestions before making a new one, as yours may be a duplicate.
• I acknowledge that all my contributions will be made under the project's license.

Notes:

New features added: others/armstrong_number.cpp: Added a program to check if a number is an Armstrong number, including functions isArmstrong to determine if a number is an Armstrong number and printArmstrongResult to print the result.