Add Singly Linked List implementation in java

[sanavi-rahane]

This pull request adds the implementation of a Singly Linked List in Java.

Features included:

• Node class to store data and pointer to the next node.
• Operations:
  1. Insert at beginning, end, and specific position
  2. Delete from beginning, end, and specific position
  3. Display the linked list

This implementation is a basic demonstration of linked list operations in Java for educational purposes.