Added Maximum width of Binary Tree code

[priyanshu-singh18]

This cpp class implements the maximum width of a tree among all levels

Description

your discription.

Checklist:

• [x] Code contain Problem statement, examples test cases.
• [x] My code follows the style guidelines(Clean Code) of this project
• [x] I have performed a self-review of my own code
• [x] Explained Detailed approach of Solution
• [x] I have commented on my code, particularly in hard-to-understand areas
• [x] Performed Time complexity analysis of the algorithm used in code