Added solution to maskify string

[Hackerbone]

Description

enter here if you have any details

Program Name -Create a function that takes a string, transforms all but the last four characters into "#" and returns the new masked string.
Issue No.- #313

Type issue number after hash(#)

Checklist(self check)

• [x] Yes, this task assigned to me.
• [x] My code follows the style guidelines(Clean Code) of this project
• [x] I have performed a self-review of my own code
• [x] My Filename is in camelCase format
• [x] I have added Problem statement, Problem link in file.

[Hackerbone]

Pls merge @aayushi-droid

[Hackerbone]

Do assign task completed tag ! Thanks 👍