#3245 Added functionality to find the middle node of singly linked list

[Tarunbot]

#3245

so here i actually implemented the functionality using slow and fast pointer to find the middle node so how it will work:- So basically this function will return the middle node of the singly linked list. if Linked list size is odd----->it will return the middle node else if Linked List size is even ---->it will return the first node from the two middle nodes.

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[github-actions[bot]]

Please reopen this pull request once you commit the changes requested or make improvements on the code. If this is not the case and you need some help, feel free to seek help from our Gitter or ping one of the reviewers. Thank you for your contributions!