Add Exercise Questions for String Operation in JavaScript

[Swap76]

Add the Exercise question for String Operation in docs/Exercise/Javascript_Basics/string_operation.md which can be solved using JavaScript

The question can be open-ended or a task to complete to learn the concept

[Ahmed-Elbessfy]

what do you mean with string operation? do you mean concatenation?

[Swap76]

@Ahmed-Elbessfy Yes Concatenation or any other thing like manipulation etc.

[Ahmed-Elbessfy]

OK I will make a tut for that

[Ahmed-Elbessfy]

check PR #331