Add Two Sum problem

**Is your feature request related to a problem? Please describe.**
Add two sum problem in java in Data Structures Folder.

**Describe the solution you'd like**
Problem Statement :
Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

You can return the answer in any order.
Example 1:

Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Output: Because nums[0] + nums[1] == 9, we return [0, 1].
Example 2:

Input: nums = [3,2,4], target = 6
Output: [1,2]
**Describe alternatives you've considered**
Leet Code question no 1

**Additional context**
Add any other context or screenshots about the feature request here.
Hi I am a LGM SOC participant & I would like to work on this issue in Java language. It would be great if you could assign this to me.

### Programming language

- [ ] C
- [ ] C++
- [x] Java
- [ ] Python