Add "Reverse String" Java Problem

[Diwakar-Gupta]

Issue Description:

This proposes adding the Reverse String problem to our Java code repository.

Problem Statement

You can find the problem statement here

Implementation

Please read Contributing to Java Problems to get started with how to create new java problem and test for the same.

Note

For this problem you have to create a new folder with name problem26 inside folder javaProblems

[PulsatingGenius]

i can do this please assign it to me.