Added linked_list_sort to the sorting folder

[SivaPA08]

This contribution implements a C++ program to sort a singly linked list using the Merge Sort algorithm. The program provides the following functionality:

mid function: Identifies the middle node of the linked list using the slow and fast pointer approach.
mg function: Merges two sorted linked lists into a single sorted list.
sortList function: Implements the Merge Sort algorithm to sort the linked list.
push function: Adds a new node with a specified value to the front of the linked list.
Main function: Demonstrates the program by creating a linked list, sorting it, and displaying the sorted result.
This code serves as an educational example of how Merge Sort can be applied to linked lists, showcasing important concepts like recursion, pointer manipulation, and divide-and-conquer strategies.