feat: Add 4Sum Leetcode solution in java

[RoshanMhatre]

Is your feature request related to a problem? Please describe. The solution for 4 Sum is not present right now.

Describe the solution you'd like I want to add the most optimized solution for it in Java and C++

Programming language

• [ ] C
• [x] C++
• [x] Java
• [ ] Python

Please assign this issue to me and add Hacktoberfest label to it.